The situation whereby an employee elects to resign and terminate his relationship with the employer by reason of the conduct of the employer.

Substantial performance describes a situation where a contracting party has performed enough of its obligations that the contract is treated as effectively completed, despite minor defects or omissions. In practice, it limits a counterparty’s ability to treat the contract as repudiated and instead confines them to a claim for damages or a price adjustment. In England and Wales and Northern Ireland, the concept is rooted mainly in contract case law (notably in building and services contracts), and is used to distinguish between a breach that goes to the “root” of the contract and lesser, remediable failings. Courts assess substantial performance fact‑sensitively, looking at the extent of non‑performance and its impact on contractual benefit. In Scotland, similar ideas arise under material breach and retention of performance, rather than a freestanding doctrine of substantial performance, but the practical effect is often comparable. In Ireland, the concept is likewise developed through case law, particularly in construction and commercial contracts, and operates similarly to England and Wales. Across all jurisdictions, parties commonly address substantial performance expressly through completion, certification and payment provisions.

A unilateral mistake arises in contract law where only one party is mistaken about a fundamental term or assumption, such as the identity of the other party, the nature of the contract, or a key price or quantity, and the other party knows or is taken to know of that mistake. It is not generally defined in legislation, but developed through case law across England and Wales, Scotland, Northern Ireland and Ireland, with broadly similar principles.Unilateral mistake may render a contract void or voidable in narrow circumstances, particularly where there is a “mistake as to terms” evident from the written agreement, or mistaken identity in face‑to‑face or distance transactions. Common examples include mis‑priced tenders, erroneous bids at auction, and mis-signed deeds.Courts distinguish unilateral mistake from common or mutual mistake and are slow to grant relief where the error is merely about commercial value or arises from a party’s own negligence. Remedies include rescission, rectification (where the written document fails to reflect the agreed terms), or refusal of specific performance. In practice, unilateral mistake is often raised in disputes over contract formation, enforceability, and mis-signed documents, and in negotiations on allocation of risk through entire agreement, non-reliance and exclusion clauses.

Business liability is liability that arises either from things done or to be done in the course of a business, or the occupation of premises used for business purposes of the occupier. Clauses that seek to exclude or restrict business liability are subject to controls under the Unfair Contract Terms Act 1977.

A contract under which one party purchases the right (but not the obligation) to acquire an asset or instrument from a seller at a specified price or by calculation of a pre-determined formula at or by a specified time in the future.

An annuity contract purchased from a dependants' unsecured pension fund held under a money purchase arrangement that provides that dependant with an income for a term of no more than five years (not reaching to or beyond their 75th birthday), and which meets the conditions under the Finance Act 2004.

A number of different kinds of engineer may be required, and appointed, depending on the nature of a construction project. These may include: • civil engineer • structural engineer • services engineer or mechanical and electrical (M&E) engineer In the FIDIC contracts, the Engineer is a defined role with contract administration and certification responsibilities.

The time by which contractual completion of unaltered work is extended.

Initial commission on a regular premium contract paid on an indemnity basis is subject to an earnings period. If the premiums are not maintained for the whole of the earnings period, the adviser is required to repay that portion of the initial commission that remained unearned when premiums ceased to be paid.

A clause, usually in a sub-contract, whereby one party is only obliged to pay the other if payment has been received from a third party. Ineffective under HGCRA 1996, s 113 except where the reason for non-payment is the insolvency of the third party.

A multilateral system, operated by an investment firm or market operator, which brings together multiple third-party buying and selling interests in financial instruments (in the system and in accordance with non-discretionary rules) in a way that results in a contract. (Definition from article 2(1)(14) of Retained Regulation (EU) No 600/2014 (UK MiFIR).

A claimant may be under a duty to mitigate their loss if there is a breach of contract or a tort is committed. The effect of a failure to mitigate is that the claimant cannot recover damages in respect of the portion of their loss that is attributable to their own conduct or lack of it.