When delays arise on a construction project, the question of who is responsible, and to what extent, can become highly contentious. That complexity only deepens when concurrent delay is involved: a situation where both the employer and the contractor are responsible for overlapping delays that affect the project’s critical path.
In these cases, the legal landscape can feel anything but straightforward. While some courts treat concurrent delay with caution, others have laid down contrasting rulings, particularly when comparing decisions across jurisdictions. Contracts may attempt to allocate the risk, but the enforceability and interpretation of those clauses vary.
In this article, we explore what concurrent delay means in construction, how the courts have approached it in England, Wales, and Scotland, and what contractors and employers should consider when navigating this complex issue.
What is Concurrent Delay?
Concurrent delay occurs when two or more delay events, caused by different parties, overlap in time and both impact the project’s completion date. In the context of construction, this typically means that one delay is the contractor’s responsibility, while the other is the employer’s.
To be classified as a concurrent delay, both events must affect the critical path of the project. In other words, each delay must, on its own, have the potential to delay completion. If only one delay is critical while the other affects non-critical activities, it’s unlikely to qualify as true concurrency.
It’s worth distinguishing between two key concepts here:
- Concurrent delay, where the delays happen at the same time.
- Sequential or overlapping delays, where causes arise close together but not simultaneously.
Understanding the difference is vital, as it influences how liability is assessed and whether the contractor is entitled to an extension of time or relief from liquidated damages.
True Concurrent Delay is Rare
While the term concurrent delay is widely used, true concurrence, where two events of equal causative potency occur at exactly the same time, is relatively rare. More often, what we see in practice is a situation of concurrent effect, where delayed events from both the contractor and the employer are close in time and appear to have overlapping consequences on the programme.
This distinction matters. In many cases, what is labelled as a concurrent delay is, on closer analysis, a dominant delay by one party, with the other having only a marginal or non-critical impact. Courts and adjudicators increasingly examine the sequence, duration, and criticality of the events in question to determine whether both were genuinely causative of delay.
Several cases have grappled with these complexities. One of the most frequently cited is Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd, which established that if there are two concurrent causes of delay, one of which is a Relevant Event under the contract (e.g. an employer risk event), the contractor may still be entitled to an extension of time, even if they also contributed to the delay.
However, later judgments have introduced more nuanced interpretations, emphasising the need for factual precision and careful analysis. The legal position continues to evolve, particularly as the courts seek to balance fairness with contractual risk allocation.
Parties Can Agree How to Deal with Concurrent Delay
Given the complexity and uncertainty that often surrounds concurrent delay, parties to a construction contract are increasingly looking to manage the risk through express contractual provisions. While the common law position provides a framework, it is open to the parties to agree in advance how concurrent delay will be treated and who should bear the consequences.
Some standard forms of contract address concurrency directly. For example, NEC4 allows the project manager to assess an extension of time and compensation event together, taking account of all effects, including those caused by the contractor. JCT contracts, on the other hand, are less prescriptive, leaving more room for interpretation and dispute.
Where contracts remain silent on concurrency, courts will revert to established legal principles to determine entitlement. However, where provisions exist, such as clauses excluding extensions of time for concurrent delays caused by the contractor, they are likely to be upheld, provided they are clearly drafted and not contrary to public policy.
Ultimately, the allocation of risk for concurrent delay is a matter of negotiation. But for any clause to be effective, it must be unambiguous, well-integrated into the contract’s overall risk structure, and reflective of the parties’ intentions. This makes early legal input essential during contract formation, rather than relying on dispute resolution later.
The Practical Assessment of a Contractor’s Entitlement
When claiming for an extension of time due to concurrent delay, a contractor must do more than simply identify overlapping events. They must demonstrate that the employer-responsible event had a real and critical impact on the completion date, not merely a theoretical one. This requires a robust, evidence-based approach to delay analysis.
The Society of Construction Law’s Delay and Disruption Protocol provides useful guidance here. It recommends that delay analysis should be prospective (forward-looking) where possible, assessing the likely impact of events at the time they occurred, rather than relying solely on retrospective assessments after the fact. The goal is to understand how the project was actually managed and how each delay influenced progress on the critical path.
A well-prepared claim will typically include:
- A clear and detailed programme showing the critical path;
- Evidence of when each delay event occurred and its impact;
- Explanation of why the employer-responsible event materially contributed to the delay.
- Justification for any extension of time requested.
Importantly, courts and adjudicators will look closely at the contractor’s conduct. Did they mitigate delays where possible? Were they already behind schedule when the employer event occurred? If so, they may find that the contractor’s entitlement is limited or extinguished entirely.
Clarity, transparency, and a methodical approach to delay analysis are essential to proving entitlement in a concurrent delay situation.
How Do the Courts Approach Concurrency?
The courts in England and Wales have wrestled with the concept of concurrent delay for decades. One of the most influential cases is Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd [1999], which established a now widely cited position: if there are two concurrent causes of delay, one a Relevant Event under the contract and one not, the contractor is entitled to an extension of time, but not to loss and expense.
This Malmaison approach effectively allows time relief without monetary compensation, balancing the prevention principle with contractual fairness. It has since been endorsed in several cases, including Walter Lilly & Co Ltd v Mackay [2012], which confirmed that the contractor should not be penalised with liquidated damages where delay is partly the employer’s fault.
However, courts continue to scrutinise whether true concurrency exists. In Saga Cruises BDF Ltd v Fincantieri SpA [2016], the court took a more restrictive view, emphasising the need for rigorous proof that both delays were independently effective and impacted the critical path.
English law remains resistant to apportioning delay between parties unless expressly allowed by contract. Instead, the focus lies in establishing which events are causative and how they interact. The Malmaison principle holds, for now, but its application requires careful and factual analysis in each case.
The Case Law: Scotland
In contrast to the English courts, Scottish law has shown a greater willingness to apportion liability in cases of concurrent delay. The leading authority is City Inn Ltd v Shepherd Construction Ltd [2007] and its subsequent appeal [2010], which marked a significant divergence in judicial approach north of the border.
The dispute centred on delays to a hotel construction project in Glasgow, where both employer-driven design changes and contractor inefficiencies were found to have caused delay. The court acknowledged the presence of concurrent causes and decided that a fair and reasonable apportionment of responsibility was appropriate.
The result was that the contractor was awarded a partial extension of time, reflecting the judge’s assessment that both parties had contributed to the delay, but not equally. Importantly, this was not a mechanical calculation but a fact-sensitive judgment, weighing the relative impact of each cause.
This approach attracted both interest and criticism. While it offered a more flexible and arguably equitable way to deal with concurrency, it stood at odds with the more rigid stance adopted in England and Wales. The City Inn case remains good law in Scotland and continues to influence how concurrency is argued and assessed in Scottish courts.
Rejection of Apportionment in England and Wales
While the City Inn case in Scotland opened the door to apportioning delay between parties, the courts in England and Wales have firmly shut it. English law continues to reject apportionment as a basis for resolving concurrent delay, unless expressly provided for in the contract.
This position was reaffirmed in Adyard Abu Dhabi v SD Marine Services [2011], where the court found that where concurrent causes of delay exist, only one of them can succeed in law. If the contractor’s delay would have occurred regardless of the employer’s breach, the contractor may not be entitled to time relief at all.
Similarly, in Saga Cruises BDF Ltd v Fincantieri SpA [2016], the court declined to divide responsibility for concurrent delay between the parties, instead requiring the contractor to prove that the employer’s delay was the effective cause of the critical path delay.
The result is a clear judicial stance: apportionment has no place in English law unless the contract allows for it. Instead, the courts apply a set of causation-based principles to determine liability. These include the prevention principle, the obverse problem, and the ‘but for’ test, each of which we’ll explore in more detail below.
Prevention Principle
The prevention principle is a long-standing doctrine in English law. It holds that a party cannot enforce a contractual obligation if they have prevented its performance. In the context of construction, this often arises where the employer’s actions, or inactions, delay the contractor’s progress.
If the employer is responsible for a delay that affects completion, and the contract does not permit an extension of time for that event, the prevention principle may render liquidated damages unenforceable. This is because the employer cannot insist on timely completion if they have obstructed it.
To mitigate this risk, modern contracts include extension of time provisions that allow for time relief where employer delay occurs, even where it overlaps with contractor delay. This helps preserve the enforceability of liquidated damages by ensuring that the contractor is not penalised for time lost due to the employer’s own breach.
However, invoking the prevention principle is not straightforward. The contractor must show that the employer’s conduct was a real and effective cause of delay, and that no contractual mechanism existed to address it. This reinforces the importance of clear drafting and timely programme updates to ensure all delay causes are properly documented and allocated.
Obverse Problem
The so-called obverse problem arises from the difficulty of allowing both parties to succeed in a claim for the same period of concurrent delay. If the contractor seeks an extension of time due to the employer’s delay, while the employer simultaneously claims damages for the contractor’s delay during the same period, the two positions are logically incompatible.
In English law, the courts resolve this by requiring a clear causative link to be established. Only one party’s delay can be treated as the effective cause for legal purposes. This means that even where delays appear concurrent, the court will determine which event had the greater or overriding impact on the critical path.
This creates a strategic challenge for claimants. Both employers and contractors must present compelling delay analysis and narrative evidence to demonstrate that their opponent’s delay was not just present, but decisive. Simply pointing to the overlap is not enough.
The obverse problem also underpins the courts’ rejection of apportionment. Rather than splitting liability, the preference is to identify a single, legally dominant cause, even in complex, multi-factorial situations.
‘But For’ Causation
The ‘but for’ test is a fundamental principle of causation in English law. It asks: but for the breach or event in question, would the loss or delay still have occurred? If the answer is yes, the event is not considered a legally effective cause.
In the context of concurrent delay, this test is often decisive. If a contractor claims an extension of time due to an employer delay, they must show that but for that employer delay, the project would have been completed sooner. If the contractor’s own delay would have caused the same outcome anyway, the claim may fail, even if both delays appear to overlap.
This approach reflects the courts’ focus on identifying the dominant or operative cause of delay, rather than simply recognising co-existing events. It also places a high evidential burden on the claiming party to show that the other side’s conduct was not just present, but necessary to the outcome.
The ‘but for’ test can be harsh in practice, particularly where the evidence is finely balanced or where records are incomplete. It reinforces the need for clear, contemporaneous documentation and rigorous programme management to establish causation with confidence.
The Future of Concurrency
The legal treatment of concurrent delay remains unsettled in some respects, and continues to evolve through case law. While the principles established in Malmaison, Walter Lilly, and Saga Cruises remain influential in England and Wales, later decisions suggest a trend toward stricter evidential standards and more forensic scrutiny of delay claims.
One example is North Midland Building Ltd v Cyden Homes Ltd [2018], where the Court of Appeal upheld a contractual clause that excluded time extensions for concurrent delay caused by the contractor. The judgment confirmed that parties are free to allocate concurrency risk as they see fit, and that clear drafting will be enforced, even where it appears to disadvantage one party.
This has significant implications. It signals a judicial willingness to uphold express terms on concurrency, moving away from default reliance on prevention principles or implied fairness. In turn, it places greater pressure on parties to consider concurrency risk at the contract negotiation stage, rather than in post-dispute argument.
Meanwhile, the Scottish courts have continued to support apportionment, and the divergence in approach may eventually be tested at a higher level. Until then, parties operating across both jurisdictions must remain alert to the forum-specific rules that govern concurrent delay claims.
Looking ahead, we may see further case law refine what counts as true concurrency, how causation is assessed, and to what extent bespoke contract terms can override common law principles.
Practical Considerations
Whether you’re an employer, a contractor, or a contract administrator, concurrent delay is not just a legal puzzle, it’s a practical risk with financial and reputational consequences. Addressing it proactively can reduce the likelihood of disputes and strengthen your position if one arises.
For contractors, the key is documentation. Maintain clear, up-to-date programmes, record all relevant events contemporaneously, and ensure that any claims for extensions of time are fully supported with evidence. Establishing the critical path impact of employer-driven delays is essential, especially where your own delays are also in play.
Employers should focus on contract drafting. If you wish to limit the contractor’s entitlement to time or cost relief in concurrent delay situations, this must be clearly set out in the contract. The courts will generally uphold such clauses, provided they are unambiguous and fairly incorporated.
Both parties should also consider whether the contract allows for neutral expert analysis, such as using delay analysts or independent adjudicators with experience in concurrency. These professionals can help unpick complex factual scenarios and may offer a route to resolution without the need for costly litigation.
Ultimately, concurrency is as much about strategy and foresight as it is about law. Identifying and allocating the risk early, through well-drafted contracts and disciplined project management, remains the most effective way to stay ahead of potential disputes.
Navigating Concurrency with Confidence
Concurrent delay is a complex and evolving area of construction law, one that calls for careful contractual planning, precise programme management, and strategic legal insight. Understanding how concurrency is treated in your jurisdiction is essential to protecting your position, whether you’re drafting contracts, managing a live project, or facing a dispute.
Our construction solicitors help construction professionals navigate these challenges with clarity and confidence. If you’re dealing with a potential concurrent delay issue or want to ensure your contracts are fit for purpose, get in touch with our construction law team today.
