Concurrent delay is complex, controversial and rarely dealt with in contract conditions (even FIDIC leaves it to special conditions). But before you can begin to grasp the issues in North Midland v Cyden let’s review some basic principles:
The Prevention Principle
“The essence of the prevention principle is that the promisee [ie the employer] cannot insist upon the performance of an obligation which he has prevented the promisor [ie the contractor] from performing….” Multiplex v Honeywell 
In practice this means “the employer cannot hold the contractor to a specified completion date, if the employer has by act or omission prevented the contractor from completing by that date. Instead, time becomes at large and the obligation to complete by the specified date is replaced by an implied obligation to complete within a reasonable time. The same principle applies as between main contractor and sub-contractor.” Multiplex at 
Why does it matter in the context of concurrent delay? “It is in order to avoid the operation of the prevention principle that many construction contracts and sub-contracts include provisions for extension of time. Thus, it can be seen that extension of time clauses exist for the protection of both parties to a construction contract or sub-contract.” Multiplex at 
Concurrent delay is
“a period of project overrun which is caused by two or more effective causes of delay which are of approximately equal causative potency” John Marrin QC article
Concurrent delay is treated under English/Welsh law as providing the contractor with time (and so avoiding delay damages) but not money. Under Scots Law the consequences on time and money are apportioned.
In Jerram Falkus the court said if there were two concurrent events, one the contractor’s fault the other said to trigger the prevention principle, “the principle would not… be triggered… [as] the contractor could not show that the employer’s conduct made it impossible for him to complete within the stipulated time.” 
North Midland v Cyden
There has long been a debate among lawyers as to whether the contract administrators should use their discretion to determine any extension of time based on all the circumstances – including overlapping delay events – or whether the contract should define concurrent delay and pass the risk to the contractor.
In North Midland, the parties amended the standard JCT contract to require:
- the contractor to make reasonable and proper efforts to mitigate delay [2.25.3] and
- ‘any delay caused by a Relevant Event which is concurrent with another delay for which the contractor is responsible should not be taken into account.'[126.96.36.199(b)]
In the High Court, the judge said that the contract was “crystal clear”. He said “there is no rule of law… that prevents the parties from agreeing that concurrent delay should be dealt with in any particular way….” aka
Do not whine. Read before you sign.
Party autonomy and freedom of contract is paramount.
In the Court of Appeal, Coulson LJ said that the clause was “unambiguous. It plainly seeks to allocate the risk of concurrent delay to the [contractor].” The court listed five reasons why the prevention principle would not ‘rescue’ the contractor from a clause to which it had freely agreed:
- the prevention principle is not an overriding rule.
- it does not apply on the facts as the contract provided for an extension for the employer’s acts
- it has no connection with the issues on concurrent delay
- the added clause [188.8.131.52(b)] was intended to reverse a specific case, not the prevention principle
- the parties can contract out of the prevention principle and clearly had!
The probable result of this case is that lawyers will add clauses into construction contracts passing the risk of delays caused by employer events to the contractor, where there are concurrent contractor delays.
The definite results of that approach are that:
- the clause will have a significant impact on passing risk of delays to the contractor. It is extremely rare that delay events occur in isolation.
- contract administrators may find it hard to extricate the employer events for which the contractor no longer gets time (due to concurrent contractor delays) from those for which the contractor is entitled to an extension.
- the contractor will be even more keen to avoid conditions precedent on extensions (which could futher reduce its right to relief) and delay damages (which are now more likely to apply).
Cases: Multiplex Constructions (UK) Ltd v Honeywell Control Systems Ltd (No. 2)  EWHC 447; North Midland Building Ltd v Cyden Homes Ltd  EWCA Civ 1744