Paying to speed up, and constructive acceleration
One is a negotiation with a price attached. The other is a claim built on a refusal, and the two are confused often enough to be expensive.
QScope Team · 16 March 2026 · 5 min read
A job is running late. The employer needs it finished on the original date. The contractor can get there with more labour, longer hours and out-of-sequence working, all of which cost money.
Agreed acceleration
The clean version. The parties agree a scope of acceleration measures, a price and a revised date, and record it. It is a separate agreement sitting alongside the contract.
What makes it work is that everything is settled in advance: what will be done, what it costs, what happens if it does not achieve the date, and what happens to any outstanding extension of time claims.
Most standard forms do not allow instructed acceleration
JCT has no general power for the contract administrator to instruct the contractor to accelerate. There is provision for the employer to invite a quotation for acceleration, which the contractor may decline.
That matters because an instruction issued as though acceleration could be ordered is not an instruction the contractor must obey, and the cost consequences of complying with it are then unclear.
Constructive acceleration
The harder claim. The contractor is entitled to an extension of time, applies for it, and it is refused or not decided. Facing liquidated damages, the contractor accelerates to protect itself and then claims the cost.
To succeed it generally has to show that it was entitled to the extension, that the entitlement was wrongly refused or not assessed, that it was reasonable to accelerate in response, and that the costs were actually incurred and reasonable.
Each of those is contestable, and the claim tends to be difficult in England and Wales. It is not impossible, but it is a long way from being a mechanism.
What a certifier should take from that
Assess extension of time claims within the contractual period and record the reasoning. A certifier who sits on a claim is not maintaining a neutral position; they are creating the conditions for a constructive acceleration argument and, on some analyses, risking time being set at large.
Costing it
Acceleration costs are not prolongation costs. They are additional resource, premium time, out-of-sequence inefficiency and sometimes plant hired specifically. They arise while the works are still running, not at the end.
Record them separately as they are incurred. A cost that only becomes visible in the final account, after the acceleration worked and the job finished on time, is a cost that looks retrospective however honestly it was spent.
The realistic advice
If acceleration is needed, agree it. Write the scope, the price and the effect on existing claims into a short document. The alternative is that somebody accelerates anyway and both parties argue about it for a year, which costs more than the acceleration did.
QScope keeps the extension of time register and the loss and expense heads separately, so an acceleration agreement is recorded as what it is rather than absorbed into a delay claim.