The Liberal Democrats are preparing to stand aside to allow ex-Tory Dominic Grieve a clear run in an upcoming general election, in the first sign of a possible Remain alliance.

Mr Grieve, who was sacked by Boris Johnson for rebelling against a no-deal Brexit, said the Lib Dems have agreed to not to field a candidate in his Beaconsfield constituency, to avoid splitting the pro-EU vote.

Talks have been underway for months between the Remain-backing parties, after the success of an electoral pact in the recent Brecon and Radnorshire by-election, where Plaid Cymru and the Greens stood aside to allow for a Lib Dem victory.

Heidi Allen, an ex-Tory MP who is helping to coordinate the efforts, told supporters that the alliance had up to 100 constituencies in its sights.

Mr Grieve, a former attorney general, told The Sunday Times: “If there is going to be a general election prior to Brexit being concluded my view is that, in those circumstances, if I can’t stand as a Conservative candidate I will stand as an independent.

“It’s up to other political parties to decide whether they wish to put up a candidate. My understanding is that the Liberal Democrats will decide not to do so, for which I am grateful.

“I believe that will be helpful. I have also had supportive emails from people who voted Labour in 2017.”

Rob Castell, the prospective Lib Dem candidate, confirmed the decision on Twitter, writing: “Yeah it’s true #remainalliance.”

Mr Grieve won the Buckinghamshire seat for the Conservatives in 2017 with a majority of more than 24,000, while the Lib Dems trailed Labour in third place with just 4,448 votes.

A Lib Dem source told The Independent: “Given our commitment to stop Brexit, we are working to make sure we have the maximum number of Remainers in parliament.

“In most places that will be the Liberal Democrats. So, it’s fair to say that there are a lot of these discussions happening across the country. In this instance, as with other seats, it’s too early to say an agreement is a done deal.”

It comes as the Westminster parties scrambled to get ready for a looming election, a prospect which appears almost inevitable after Mr Johnson wiped out his own Commons majority by sacking 21 Tory no-deal rebels.

Opposition parties refused to allow him to trigger an early election last month, insisting that a poll could not take place until the threat of a no-deal Brexit on 31 October had been taken off the table.

Ms Allen recently told supporters of the Unite to Remain alliance: “Ahead of an inevitable general election we are helping to form cross-party agreements whereby Remain-supporting parties will agree that there will be only one Remain general election candidate in key constituencies.