UKIP's only MP Douglas Carswell has quit the party.
Mr Carswell will sit in the House of Commons as the independent MP for Clacton.
Mr Carswell said he was leaving "amicably" and that there will be no need to call a by-election in his Clacton constituency as he will not be rejoining the Tories or switching allegiance to another party.
It comes after a public disagreement with UKIP's biggest financial backer Arron Banks, a close ally of former leader Nigel Farage, who suggested this month that he could trigger a by-election in Clacton using a recall petition and stand against Mr Carswell.
Carswell has jumped before he was pushed. He was never UKIP and sought to undermine us. He should have gone some time ago.
— Nigel Farage (@Nigel_Farage) March 25, 2017
Announcing his resignation on his blog, Mr Carswell said UKIP has now achieved its goal of getting Britain out of the European Union, with Prime MinisterTheresa May poised to trigger Article 50 to formally begin Brexit on Wednesday.
He said while UKIP has not won many seats in Parliament, "in a way, we are the most successful political party in Britain ever".
Mr Carswell paid tribute to party members and supporters, adding: "Like many of you, I switched to UKIP because I desperately wanted us to leave the EU.
"Now we can be certain that that is going to happen, I have decided that I will be leaving UKIP.
"I will not be switching parties, nor crossing the floor to the Conservatives, so do not need to call a by-election, as I did when switching from the Conservatives to UKIP.
"I will simply be the Member of Parliament for Clacton, sitting as an independent.
"I will leave UKIP amicably, cheerfully and in the knowledge that we won."
UKIP leader Paul Nuttall, who in February failed to get elected as an MP, said the party has not benefited "financially or organisationally" from Mr Carswell's presence in the House of Commons and so his departure would make "no difference" to his reform agenda.
"This is not a surprise," the leader said.
