The Mayor of London, Boris Johnson has written a scathing attack of Ed Miliband’s energy credentials, saying the Labour leader in power would be “like a turbine inert on a windless day”.

Writing in the Telegraph he chastises the former Energy Secretary for failing to muster any enthusiasm for a scheme to make London homes more energy efficient during their last official meeting: “He wasn’t remotely interested. He didn’t want to talk about retro-fitting and, as I gabbled away about a new legion of ‘boiler bunnies’ bouncing up to your door, I was aware that a deep tranquillity had settled on the minister.”

He goes on to berate Labour’s “Wonga-like offer” of an energy price freeze: “[Ed Miliband] says he will imitate the catastrophic policies of the emperor Diocletian, by imposing a price freeze on energy bills for the 20 months succeeding the election. And, er, then what? Well, then the energy companies will of course recoup their losses by whacking the prices jaggedly upwards again.”

Mr Johnson claimed the “meddling jiggery-pokery” sends out the “worst possible message to anyone thinking of investing in this country”.

Last week shares in energy suppliers Centrica and SSE took a dive following Mr Miliband’s announcement of the price freeze policy.

However the price freeze plan seems to have gone down well with members of the public: a YouGov poll for the Sunday Times gave Labour an 11-point lead over the Conservatives with support rising 5% after the conference to its highest level (42%) since June.