A Labour peer has resigned from the party after announcing that he will vote for the Liberal Democrats in this week's European Parliament elections.
Michael Cashman, a prominent LGBT campaigner and former Labour MEP, said he "can't trust" Jeremy Corbyn and his team on Brexit and would be backing the Liberal Democrats because of their "absolute consistency" on the issue.
A number of elected officials from the main parties have now said they are unable to vote for their own party in the EU elections because of the leadership's position on Brexit.
Mr Corbyn has come under pressure for refusing to commit to another Brexit referendum and has seen many of his party's supporters switch to the Liberal Democrats.
The latest polling suggests Labour is on course to receive just 13 per cent of the vote in Thursday's elections, compared to the Liberal Democrats' 19 per cent.
As the main parties haemorrhage support, the Conservatives are polling at just 7 per cent having significantly lost ground to Nigel Farage's Brexit Party, which is on course to win the elections with 37 per cent of the vote.
Lord Cashman, who sat as a Labour MP between 1999 and 2014, used his Twitter page to announce that he "Will not be voting for the Labour Party".
Referring to journalist Matthew Parris, who said he would also be voting Lib Dem for this first time ever, the peer wrote: "I can’t trust Corbyn or the people around him on the defining issue in postwar Britain so on Thursday I will not be voting for the Labour Party. As Matthew Paris [sic] said, I am not a Liberal Democrat, but I support their absolute consistency. Voting Lib Dem in the EU elections."
He added: "I think I’ve just resigned from the Labour Party by declaring that I will support the Liberal Democrats in the European elections."
He had earlier told his followers to "vote wisely on Thursday", suggesting they should back a party that wants another referendum. He said: "The only way to resolve the most important issue facing this country and dividing it is with a final say on Mrs May’s deal. "
A Labour spokesperson said they did not comment on individual membership cases.
Conservative peer Andrew Cooper, a former director of strategy to David Cameron, also announced that he would be voting for the Liberal Democrats, and swiftly had the Tory whip withdrawn. He follows in the footsteps of Michael Heseltine, the former Tory deputy prime minister, who said last weekend that he would be voting for Sir Vince Cable's party.
Lord Cooper said: "I have come to the same conclusion as Michael Heseltine, for exactly the same reasons - and will be voting Lib Dem in Thursday's European Parliament elections."
Warning the Conservatives to ditch their current Brexit policy, he added: "I think the party is going to plunge into oblivion if it continues on the path of trying to out-Brexit the Brexit Party. I think the right thing to do in this election is to vote for the party that believes in a referendum and giving a chance to look again at the whole question.”
A Conservative spokesperson said: "Publicly endorsing the candidates of another party is not compatible with taking the Conservative whip in parliament.
"As a result, the chief whip in the House of Lords has informed Lord Cooper of Windrush that he will have the Conservative whip suspended.
"This will be reviewed if he is willing to support Conservative candidates at future elections."
Earlier in the week, Lord Heseltine wrote in The Sunday Times: “I cannot, with a clear conscience, vote for my party when it is myopically focused on forcing through the biggest act of economic self-harm ever undertaken by a democratic government".
A third peer, former cabinet secretary Gus O'Donnell, also announced his support for the Lib Dems.
The former head of the civil service, who sits as a crossbencher in the House of Lords, said he believed another referendum was the only way "to bring to country" together and that he would back Remain in such a vote.
Admitting it felt "very strange" to be endorsing a political party, he wrote in The Times' Red Box: "I am extremely disappointed that while the Brexit Party is an obvious choice for dedicated Leavers the Remain vote is potentially spread across many parties.
"This is deeply disappointing and very annoying, particularly given that the Liberal Democrats seemed to be prepared to cooperate with other parties. Under the voting system used for European elections it means that the Brexit Party will do extremely well compared with the Remain parties unless supporters of the latter view vote tactically.
"This means voting Liberal Democrat in England, so that’s what I will do. I would urge all those who support Remain to do the same."