If a designer makes a mistake, when does the obligation to correct it expire? After the relevant bit is built? After practical completion? After the final certificate? Or never …
Safaris are not for the squeamish. The sight of cheetahs stalking a wildebeest who has strayed from the herd is nature red in tooth and claw. Your columnist had an unusual Christmas.

When a client finds its new office has leaking cladding, it is obliged to engage the urban equivalent of cheetahs to seek redress from anyone in sight, particularly consultants with valuable professional indemnity insurance that have drifted from the path of conventional design. The consultant that realises, after construction is complete, that something in the design may have been negligent will be condemned to sleepless nights.

In the Abbeystead case, a number of people were killed in an explosion resulting from a build-up of methane in a tunnel that was part of an aqueduct system. The judge at first instance took the view that consultants should advise former clients after final certificates had been issued if new knowledge called old decisions into question.

Although understandable as a reaction, this line of reasoning had the potential to destroy consultants as an independent professional class, and the Court of Appeal poured cold water on that idea. Since then, a number of cases have suggested that an architect owes duties to its client to review a design up until practical completion, and possibly afterwards, but certainly not beyond the final certificate.

We now have a serious judicial analysis of this area in the very recent decision of Mr Justice Dyson in New Islington & Hackney Housing Association vs Pollard Thomas & Edwards Ltd (New Law Online Case 2001222306; 8.12.2000).

The case concerned allegations of negligent design in connection with the soundproofing of flats, and, in particular, whether or not claims in contract and tort were time-barred. Such questions raise difficult issues of law, but in the course of his judgment Mr Justice Dyson also addressed some practical problems that consultants face every day.

Although understandable, this line of reasoning had the potential to destroy consultants as an independent professional class, and the Court of Appeal poured cold water on it

What should a consultant do if asked to investigate alleged deficiencies? The right response, the judge suggested, should be to refuse unless offered a fee. Although the consultant owes a duty to review its design, once that design is embodied in the structure, the duty is discharged. It would only revive if, after then, the consultant became aware of a problem before practical completion.

But after practical completion? The judge thought there would be no such duty, but in case he was wrong, it would revive only if the consultant was put on notice of a problem.

Judges, unlike consultants, can more easily hedge their bets when taking professional decisions. It is more difficult to pronounce a principle of law unfit for its purpose than a cladding design. But the uncertainty about the existence and/or scope of a duty to review a design after practical completion – when the right to vary the works has plainly gone – is worrying. What is the right answer to this conundrum? We can probably all agree, as a matter of common sense, that between completion of the design and its embodiment in the structure, the consultant should retain an obligation to review it. Once the relevant part of the works has been constructed, does the situation alter? At this stage, and before practical completion, if a design defect comes to light there is still an opportunity to put things right by a variation, and the duty surely subsists to advise the client of the problem.

But after practical completion? No power to instruct the contractor remains, although it may be possible to reach agreement about a course of action. Surely the conscientious consultant that becomes aware of a design defect would feel obliged to advise the client, even though the power to vary the works has gone.