> £700m on fish protection at Hinkley Point C. So what is the cost per fish saved? > > Asked on LinkedIn, after the fish disco post

It depends entirely on which fish count you divide by, and the answer runs from around £280,000 a fish to a few pence.

The £280k figure. This takes the whole £700m and divides it by the developer's own modelled savings of salmon and sea trout, which come to a fraction of a fish a year, plus a small number of other species. That gives roughly £280,000 per fish over 25 years. It is the number that made the headlines.

Why it is not the whole story. The £700m is not all fish money. Around £500m is the low-velocity intake heads, £150m the fish recovery and return tunnel, and about £50m the acoustic deterrent itself. The intake heads also keep the cooling system clear, and no nuclear operator wants that blocked by fish, living or dead.

The other count. The Environment Agency's research suggests something like 4.6 million adult fish a year could be lost without protection. Divide by millions and the cost falls to pounds per fish, or pence. EDF and the nuclear industry frame it by weight instead: around 44 tonnes a year without the deterrent, about one small fishing boat's catch.

Same project, two honest calculations, wildly different answers. As a QS I would want every mitigation priced on the same basis before anyone argues about it.

Where do you sit: was this money well spent, or a warning for Sizewell C?