Theresa May's joint chiefs of staff have resigned, another sign of the prime minister's power collapsing following Thursday's disastrous general election result, which saw the Conservatives lose seats.

Nick Timothy and Fiona Hill, the Downing Street aides who were infamous for running almost every aspect of the prime minister's political operation, announced their resignations on Saturday afternoon.

The pair had worked with May for years, including when she was in the Home Office, and personally played a substantial role in shaping her public persona and policy platform. Following the election result they attracted much of the blame, with ministers briefing against them and Tory MPs demanding their resignations.

Their decision to quit leaves an enormous hole in the Downing Street political operation and raises even more questions about whether May has lost the power to even choose her own advisers.

Timothy, who wrote much of the manifesto, was blamed for including the "dementia tax" policy – but in a resignation statement on ConservativeHome he insisted many other were involved in that decision.

"The Conservatives won more than 13.6 million votes, which is an historically high number, and more than Tony Blair won in all three of his election victories," he said. "The reason for the disappointing result was not the absence of support for Theresa May and the Conservatives but an unexpected surge in support for Labour."

Timothy said May understood the anti-austerity mentality that drove the surge in support for Jeremy Corbyn's party but that the Tories did not communicate this to the public.

"The Conservative election campaign, however, failed to get this and Theresa’s positive plan for the future across," he wrote. "It also failed to notice the surge in Labour support, because modern campaigning techniques require ever-narrower targeting of specific voters, and we were not talking to the people who decided to vote for Labour."