Boris Johnson has vowed to give his total support to the next prime minister, but could not resist using his penultimate speech to take a potshot at Liz Truss’s energy plans. In an attempt to shore up his legacy days before he leaves No 10, the outgoing Conservative leader hailed the government’s “accelerated, long overdue reforms” to make the UK more energy independent and announced £700m for the Sizewell C nuclear plant. But he disparaged fracking, which Truss has pledged to lift a ban on, and hydrocarbons, another energy source his likely successor wants to exploit through further drilling in the North Sea. “If we could frack effectively and cheaply in this country, that would be possibly a very beneficial thing. I’m just, I have to say, slightly dubious that it will prove to be a panacea,” Johnson said on Thursday. “I would much rather that we focused on the things where we are brilliant, and where the environmental damage is really minimal.” Johnson later added: “Tell everybody who thinks hydrocarbons are the only answer and we should get fracking and all that: offshore wind is now the cheapest form of electricity in this country … Of course it’s entirely clean and green.” The comments will be viewed as a jibe at Truss, who last week pledged to “end the effective ban on extracting our huge reserves of shale gas by fracking”, and is said to want to issue up to 130 new drilling licences for oil and gas companies to explore new fields in the North Sea. Reflecting on his future, Johnson said he was “ready to get on with life”, and he refused to be drawn on whether he would disappear quickly from politics, like David Cameron, or remain on the backbenches, as Theresa May has done. “Only time will tell, is my answer on that one,” he replied. “My intention – and what I certainly will do – is give my full and unqualified support to whoever takes over from me.” Johnson also evaded questions on whether he had any regrets about his premiership, saying he would leave it to “younger, fitter, more active journalists than me” to assess. Pressed on what message he had for people worried about paying their energy bills this winter amid rising inflation and the threat of a recession, he said people should be braced for a “very tough winter and we just have to accept that”. “We’re on your side,” he insisted, adding there would be a further package of support from the next prime minister, who will be announced next Monday and will take office the following day. The “future will be better when we’re more self-reliant” and less dependent on energy imports, Johnson predicted. After being accused by Rishi Sunak of ignoring the harms of lockdown during the Covid pandemic, Johnson said the criticism that it had caused the huge backlog of NHS surgery was an “inversion of logic”. Instead, he said, the opposite was the case; if the three national lockdowns had not been ordered, the NHS would be in an “even worse” position. Johnson will travel to meet the Queen in Balmoral to formally resign next Tuesday, with his successor formally appointed shortly after. The new prime minister will return to London to appoint a cabinet, and will then face questions in the Commons on Wednesday.