Jurisdiction(s):
United Kingdom

Key definition

Prevention principle definition

What does Prevention principle mean? In practice, the prevention principle means a contracting party cannot insist on the other party’s timely performance, or recover liquidated damages, where its own act or omission has materially delayed or hindered that performance. It is a common-law rule developed in case law (not statute), used across contract law and most prominently in construction contracts. Key effect: if the employer causes delay and the contract contains no effective extension of time (EOT) mechanism for employer‑risk events, time becomes “at large”. The contractor’s obligation is then to complete within a reasonable time, the liquidated damages regime falls away, and the employer’s remedy...

The Prevention Principle in English Construction Law: Delay Claims, Extensions of Time, Notification Time Bars, Concurrent Delay, Liquidated Damages and Time at Large

Published by a LexisNexis Construction expert

Practice notes

This Practice Note explores the meaning and nature of the prevention principle and its bearing on delay claims in construction projects. It also addresses the principle’s application to notification provisions and to concurrent delay.

The meaning and nature of the prevention principle

In brief, under English law the prevention principle means a contracting party must not impede fulfilment of a condition or the occurrence of another contingency. It is closely linked to the idea that no party may profit from its own wrong—ie it cannot rely on its own breach or act of prevention to claim a contractual right.

In the construction context, Jackson J (as he then was) in Multiplex v Honeywell provided a helpful touchstone: a promisee cannot insist on performance of an obligation it has prevented the promisor from performing. The Court of Appeal in North Midland v Cyden also offered guidance on the principle’s nature, where it had to consider whether the principle...

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Web page updated on 22/05/2026

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