Concurrent Delay: Who Keeps the Time, Who Pays for It

Concurrent delay takes up more space in delay submissions than any other doctrine, and it is misapplied in most of them. The English position is settled and deliberately asymmetric: where employer delay and contractor delay are truly concurrent, the contractor keeps its extension of time in full, but it recovers nothing for the concurrent period unless it can separate the money. Who keeps the time and who pays for it are different questions with different answers.

The working definition comes from Henry Boot Construction (UK) Ltd v Malmaison Hotel (Manchester) Ltd (1999) 70 Con LR 32.¹ Dyson J recorded the parties' agreed position: if there are two concurrent causes of delay, one of which is a relevant event and the other is not, the contractor is entitled to an extension of time for the period of delay caused by the relevant event, notwithstanding the concurrent effect of the other. The example given was exceptionally inclement weather stopping the works for a week while the contractor was, in the same week, short of labour: one cause a relevant event, one not, both operative.

Two decades of refinement have sharpened the concept rather than changed it. The definition now most often adopted is John Marrin QC's: a period of project overrun caused by two or more effective causes of delay of approximately equal causative potency, a formulation endorsed by the Court of Appeal in North Midland. The qualification matters. True concurrency requires two effective causes operating at the same time, each independently sufficient to delay completion. Delays that are sequential, delays on different paths, and contractor delay that merely coexists with an employer event without driving completion do not qualify.

True concurrency is rare; asserted concurrency is everywhere.

Walter Lilly & Company Ltd v Mackay [2012] EWHC 1773 (TCC) settled the English position on time.² Akenhead J held, at [370], that where delay is caused by two or more effective causes, one of which entitles the contractor to an extension of time as a relevant event, the contractor is entitled to a full extension of time. There is nothing in the JCT machinery that permits the extension to be discounted because the contractor was also in culpable delay: the clause asks whether a relevant event caused delay to completion, not whether it was the only cause.

The result is not generosity to contractors. It reflects the structure of the bargain: the employer accepts the risk of the events it has designated as relevant events, and the contractor cannot be held to a completion date that the employer's own acts helped to make unachievable. The Society of Construction Law Delay and Disruption Protocol, 2nd edition (February 2017), adopts the same position at Core Principle 10: concurrent contractor delay should not reduce the extension of time due.⁶

City Inn Ltd v Shepherd Construction Ltd [2010] CSIH 68 took a different road.³ The Inner House of the Court of Session held, by a majority, that where two causes of delay are concurrent and neither can be identified as dominant, the decision-maker may apportion the delay between them in a fair and reasonable way, treating the exercise as one of judgment rather than strict causation.

City Inn is regularly cited in English adjudications and just as regularly overvalued. It is a Scottish decision, persuasive authority at most, and Akenhead J expressly declined to follow it in Walter Lilly. Apportionment of an extension of time forms no part of English law. A tribunal invited to split a concurrent period sixty-forty on a contract governed by English law is being invited into an exercise the authorities do not sanction, and a responding party should say so plainly.

The extension of time protects the contractor from liquidated damages. It does not carry loss and expense with it. De Beers UK Ltd v Atos Origin IT Services UK Ltd [2010] EWHC 3276 (TCC) states the general rule: where there is concurrent delay to completion caused by matters for which both employer and contractor are responsible, the contractor is entitled to an extension of time but cannot recover in respect of the loss caused by the delay.⁴

The logic is straightforward causation. Loss and expense must be proved to have been caused by the employer event. If the contractor would have been on site for the same period in any event because of its own delay, the but-for test fails and the time-related loss is irrecoverable. Core Principle 14 of the SCL Protocol draws the same line: the contractor recovers compensation for a concurrent period only if it can separate the additional costs caused by the employer delay from those caused by its own.⁶ Untangling the compensable delay is not a pleading exercise; it is a records exercise, and it must be done head of loss by head of loss.

The contractor keeps the time. It does not, without more, get the money.

All of the above is the default position, and North Midland Building Ltd v Cyden Homes Ltd [2018] EWCA Civ 1744 confirmed that it is no more than that.⁵ The contract, a JCT Design and Build form with bespoke amendments, provided that any delay caused by a relevant event which was concurrent with a delay for which the contractor was responsible would not be taken into account in assessing the extension of time. The contractor argued that the prevention principle rendered the clause ineffective. Coulson LJ disagreed: the clause was “crystal clear”, the parties were free to allocate the risk of concurrent delay as they wished, and the prevention principle is not an overriding rule of public or legal policy capable of defeating express terms.

The practical consequence is that concurrency is now as much a drafting question as a legal one. Bespoke amendments to JCT and NEC forms routinely shift concurrency risk to the contractor, and some define concurrency so loosely that they capture delay which is merely sequential. The first task in any concurrency dispute is therefore not Walter Lilly but the contract itself: establish what the clause says, whether it adopts or displaces the default position, and how it defines the concurrency it purports to exclude.

Wherever the contractual line falls, the dispute is decided on the records. Concurrency arguments collapse or succeed on the quality of the as-built evidence and the causal analysis built on it, and the party that can demonstrate what was actually driving completion, week by week, usually prevails.