Quick answer

Approval does not relieve the party that prepared a defective drawing, which remains liable; the architect or engineer becomes liable only where it took on a checking duty, and the employer can recover its whole loss from either concurrent wrongdoer, with a contribution between them under the Civil Liability (Contribution) Act 1978

Approval, an architect's or engineer's checking or inspection of drawings prepared by a contractor or subcontractor does not, as a rule, relieve the party that prepared them from liability for a design error; the designer remains answerable, and an architect cannot delegate its design duty without the building owner's consent. What approval can do is add the professional as a second defendant, but only where it took on a checking duty. Merely transmitting drawings for comment does not create a design obligation, whereas positively accepting a design, or approving working drawings under an appointment that requires it, can. Where the employer bears the cost it can recover from the checker if the appointment imposed a duty to check that was not properly performed. Where two parties are each liable for the same damage, the claimant's recovery and each party's share depend on the established causes of action and the rule against double recovery. Section 1 of the Civil Liability (Contribution) Act 1978 permits one liable party to seek a just and equitable contribution from another liable for the same damage.