"It was Putin's invasion of Ukraine that spooked the energy markets. It is Putin's war that is costing British consumers. That is why your energy bill is doubling," Boris Johnson wrote.
Boris Johnson has admitted that energy bills will be "eye-watering" this winter - and the cost of heating is already "frightening" for some.
Writing in The Mail on Sunday, the outgoing prime minister blamed Vladimir Putin for the worsening crisis - and claimed the Russian president "likes it".
And although Mr Johnson warned the months ahead could be "very tough", he has insisted the UK's future "will be golden".
He wrote: "It was Putin's invasion of Ukraine that spooked the energy markets. It is Putin's war that is costing British consumers.
"That is why your energy bill is doubling. I am afraid Putin knows it. He likes it. And he wants us to buckle."
Mr Johnson claimed that the president believes "soft" European politicians will ease sanctions "and go begging for Russian oil and gas" as the winter sets in.
But he warned withdrawing support from Ukraine would be "utter madness" - and insisted Putin's position "grows weaker" with every passing month.
Boris Johnson met Volodymyr Zelenskyy in Kyiv on Wednesday
The Conservative government has been accused of lacking urgency with the cost of living crisis as the leadership contest between Rishi Sunak and Liz Truss continues.
However, Mr Johnson wrote: "We must, and we will help people through the crisis. Colossal sums of taxpayers' money are already committed to helping people pay their bills. That cash is flowing now - and will continue to flow in the months ahead.
"Next month - whoever takes over from me - the government will announce another huge package of financial support."
Ms Truss, who is the frontrunner to be named the next prime minister on 5 September, has said it would not be "right" to announce her full plans for tackling the crisis until the contest is over.
In his article, Mr Johnson attempted to strike an optimistic note, and said he was certain "Britain will emerge stronger and more prosperous the other side".
He later added: "We have more than enough resilience to get through the months ahead. We have shown that before.
"And we have made the long-term decisions - including on domestic energy supply - to ensure that our bounceback can and should be remarkable and that our future will be golden."
But Labour's shadow minister Pat McFadden told Sky News the PM's article "just shows how little he understands the shockwave that was sent through households around the country by Ofgem's announcement on Friday".
He added: "We are looking at energy bills of hundreds of pounds per month for households around the country and the conversation that's taking place, of course, is 'how can we afford this, what else can we cut? And for some people, it will simply be impossible."
But former cabinet minister Simon Hart, who was among those who resigned in protest at Mr Johnson's premiership, said it was "perfectly reasonable" for the PM to say the UK will bounce back.
"We started this in a reasonably strong position, thanks to some of the decisions which have been taken by Rishi Sunak, to be honest, over things like furlough.
"[So] actually we are going to be able to emerge from this in a period of months in a reasonably strong position. That's an entirely reasonable scenario."
Reports in The Sunday Telegraph suggest Ms Truss is considering cutting VAT by up to five percentage points to help consumers and businesses cope with rising costs - potentially from 20% to 15%.
A source told Sky News that Ms Truss "will consider options to help people, but it would not be right for her to announce her plans before she has been elected prime minister or seen all the facts".