Conservative civil war deepens as Boris Johnson backs MP who branded Theresa May's party a 's**t show'

Boris Johnson has thrown his weight behind the Conservative MP who branded Theresa May’s party a “s**t show”, as the Tories enter a fresh round of Brexit infighting.

The former foreign secretary credited Johnny Mercer with having “passion and determination” after he branded Ms May a “technocrat” and said her Brexit strategy would not be swallowed by the party without a “s**t fight”.

Former cabinet minister Nicky Morgan said her party is now under “existential strain”, with friendships between colleagues irreparably damaged as it squabbles over the UK’s departure from the EU.

It follows a summit in Brussels at which Ms May raised the prospect of an extension to the Brexit transition period as a way of breaking the impasse in negotiations – something both Tory Eurosceptics and remainers have attacked.

Thousands of people are preparing to march in central London this Saturday for a new Brexit vote at a demonstration jointly organised by The Independent and the People’s Vote campaign.

The Independent is also running its own Final Say campaign to demand the referendum, with more than 930,000 people having signed its petition so far.

After the searing criticism from Mr Mercer, seen as a moderate backbencher, Mr Johnson said on Twitter: “The Conservative Party is fortunate to have MPs with the passion and determination of [Johnny Mercer], his fight for veterans shows why we need more like him.”

The comments from the ex-cabinet minister, himself an ardent critic of the prime minister since quitting the cabinet over Brexit, once again underline the difficulty Ms May will have passing her plans through the Commons.

Senior backbencher Tom Tugendhat MP, seen as a key figure on the more liberal wing of the party, showed support for Brexiteer Mr Johnson’s comments on social media.

Tory MP for West Aberdeenshire Andrew Bowie warned that Scottish Conservatives would find a move by Ms May to extend the transition “unacceptable”, if it meant remaining in the EU’s Common Fisheries Policy.

But it was comments from the Tory chair of the Treasury Committee, Ms Morgan, that really laid bare the personal toll on MPs divided over Brexit.

Asked about the impact on her party’s unity, she said it is “massive”, as she attacked interventions from Mr Johnson and former cabinet minister David Davis, who is also said to be on leadership manoeuvres.

Ms Morgan went on: “I think it’s put the party under existential strain.

“I still believe ... that we absolutely can come back together after this, but it’s going to have to be because people want to do that, there are still many, many issues which unite us as Conservatives, but yes I think there are friendships and relationships that will never be healed from this in the party.”

Late on Thursday night, the Brexit-backing former party leader Iain Duncan Smith, said moving to extend the transition period would see the UK paying “tens of billions of pounds” extra to the EU.

Tory MP Nick Boles, who backed Remain in the EU referendum, said he would also oppose any extension, calling it “an absolute mile from what we were originally told was necessary”.