Remain supporting parties risk winning less than half the seats they could have done in May's European elections because they have failed to work together, Liberal Democrat leader Vince Cable has warned.
Speaking at an event to launch his party's EU election candidates in Wapping, east London, Sir Vince said he had tried to get other parties to pull together.
But Sir Vince, who is standing down as his party's leader in May, said regrettably, other parties had not joined him so the Lib Dems would instead campaign alone.
It follows a leaked document from the Change UK that revealed a plot to wipe out the Liberal Democrat party and take on all its members, donors and MPs.
It suggested that the group of Tory and Labour defectors wants directly target Lib Dem voters to compete with the centrist party on its own issues.
The Twickenham MP was clear that the only losers from that strategy would be Change UK, who have since disavowed the memo.
He told the Mirror: "The analysis shows that if we combined our efforts we would get 16 seats and if we are competing we get seven.
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"They would all be Lib Dems as it happens.
"We are the strongest of the three Remainer parties but it would be better if we weren't fragmented."
But Mr Cable said he would try and look past the conflict even though the move meant Change UK had made a "bad mistake".
He said: "They've handled the whole thing very badly, but I don't want that to get away from the fact that in the long term our interests are in the same place - grown-up politicians should continue to work together.
"We'll be campaigning against the opposition, which isn't them - it is the Brexit parties. "It's true that the Brexit parties are also divided but we should be standing together - the millions of people in this country who voted Remain would expect us to stand together.
"It has not happened ... it was not reciprocated so we're going our own way, but it's a pity."
Mr Cable said it should be remembered that the Lib Dems stood alone against Brexit from the start - just like Charles Kennedy did in the 2003.
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The Twickenham MP said: “"Without the Liberal Democrats , the campaign to Stop Brexit wouldn’t have got off the ground.
"We are proud to work across party lines to stop Brexit but it bears remembering that when we started, we stood alone.
"In Parliament, it reminded me of Charles Kennedy’s opposition to the Iraq War. We were barracked on all sides but we stood steadfast anyway.
"As with that tragedy, millions have now come round to our point of view. A clear majority of the public now supports a People’s Vote."
It comes after shock polls put Nigel Farage’s newly founded Brexit Party - who propose leaving the EU without a deal - on course to win the election, due to be held on May 23.
Elections to the European Parliament are only being held because of the governments failure to pass a withdrawal agreement in Westminster.
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Elected MEPs will sit until the UK withdraws from the EU - either with an agreement supported by Parliament or by crashing out with no deal.
Britain's membership of the union has been extended until October 31 this year.
But Mr Cable is hoping that these elections will prove support in the country to stop the UK leaving the EU.
He told members at the party's launch that "every vote for the Liberal Democrats is a vote to Stop Brexit".
He said that the last three years had been a "national humiliation"
He added: "The fact European elections are happening at all is testament to the dismal failure of Brexiters to have any common plan about what Brexit should mean.
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The election will likely be a tough one for the Lib Dems.
It comes after newly founded Remain supporting party Change UK refused to enter into an electoral alliance with the Lib Dems - despite the risk of splitting the anti-Brexit vote.
But even without the split votes, the party faces an uphill battle to reverse recent electoral losses.
In the last European elections in 2014 - held four years into its coalition with the Conservative Party - the party lost 10 seats, leaving it with just one MEP.
