A claim for restitution of overpayments under a terminated construction contract must plead a recognised ground of unjust enrichment (such as failure of basis, mistake, or duress) — it is insufficient merely to allege that payments exceeded the contractual price cap. Contractual terms that have ceased to operate upon termination cannot, on their own, form the basis for a restitutionary claim, though they may be 'relevant' to such a claim. The question whether compulsion arising from a statutory adjudication process can ground a restitutionary claim was left open.
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