Image copyright EPA Image caption Theresa May is still prepared to walk away from Brexit talks without a deal, says her former joint chief of staff

The Conservative Party should have campaigned for "change not continuity" in the general election, one of Theresa May's former leading advisers has said.

Nick Timothy told the Daily Telegraph that Downing Street was also guilty of a breakdown in communication with both the public and Whitehall departments.

The party clearly underestimated Labour leader Jeremy Corbyn, he added.

Mr Timothy resigned as the prime minister's joint chief of staff after the Tories lost their majority.

He said: "If the party retreats into a comfort zone that we don't find very challenging, I worry that we will not only fail to address the challenges the country faces but we will also increase the chances of a hard-left government in five years' time."

Mr Timothy was joint chief of staff alongside Fiona Hill, and co-wrote the Conservatives' manifesto going into the general election.

He rejected reports that Mrs May had intended to sack Chancellor Philip Hammond if she increased her Commons majority.

Mrs May is still prepared to walk away from Brexit talks without a deal, he added, but her hopes of reversing the ban on new grammar schools are over.

Image copyright PA Image caption Nick Timothy was Theresa May's joint chief of staff

Mr Timothy said plans for ministers to play a bigger part in the election campaign were overruled by party strategists.

He conceded it "probably is true that there should have been more on the economy during the campaign".

"Overall the lesson of the election for the party and for the government cannot be: 'Oh well, we tried that and we didn't win the election we were hoping for so let's not try it any more'," he said.

"If the party retreats to a much more orthodox Conservative proposition then I worry that won't be sufficient to tackle the big problems that the country has and in five years' time we do risk the election of a dangerous left-wing alternative."

Mr Timothy was interviewed by the Telegraph ahead of starting to write a weekly column for the paper.