The economics of the world’s biggest offshore wind-farm project are “on a knife-edge”, the chief executive of one of the companies behind it has warned, casting doubt on the UK government’s energy strategy.

Eon UK, the British arm of the German energy group, said the viability of its London Array project, a planned 1,000MW wind farm in the Thames estuary, had been called into question by the falling prices of oil, gas and carbon dioxide emissions permits.