Douglas Carswell will not stand in general election
Former UKIP - and now independent - MP Douglas Carswell says he thinks he will be "the first and the last UKIP MP".
The Clacton MP says he will not be standing in the UK general election - but would be backing the Conservative candidate instead.
The 45-year-old was the only UKIP candidate to be elected as an MP at the 2015 poll. He quit the party last month after falling out with its leadership.
UKIP donor Arron Banks had vowed to stand against him in Clacton.
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Mr Carswell defected from the Conservatives to UKIP three years ago but clashed with then leader Nigel Farage and other senior figures over the direction the party was taking.
UKIP leader Paul Nuttall said at the time that Mr Carswell was "committed to Brexit, but was never a comfortable Ukipper".
Mr Carswell admitted that he had been tempted to quit UKIP following last year's EU referendum - he now believes he will be "just a footnote in political history" that will say "he was the first and the last elected UKIP MP".
Saying that he feels UKIP's job is mainly done, he said: "Britain is about to become a sovereign country again - I feel I've done what I set out to do."
He now supports Theresa May, adding: "I think she will deliver the sort of Brexit I want."
Asked if he had wanted to be the Conservative candidate for Clacton, he commented: "I've never sought and never asked for the nomination.
"I very nearly announced my departure from UKIP and my intention to stand down on June 24 last year... I was quite close to doing it."
Pressed on whether he would consider a return to politics, he conceded: "Perhaps if we were dragged back into the European Union [but] that's not going to happen.
"No, I'd never rule anything out, but I genuinely would like to go on and do other things with my life."
Suzanne Evans, seen as one of Mr Carswell's former allies in UKIP, said she was "very surprised" by his decision not to seek re-election.
She told the BBC's Daily Politics it might be "a little bit premature", as the UKIP candidate for Clacton has not yet been selected.
Arron Banks - who described Mr Carswell's departure from the party as "a rare piece of good news for UKIP" - was planning to stand against him in Clacton, although it is not clear whether he would be UKIP's candidate.
After Mr Carswell's announcement, Mr Banks tweeted saying: "The Clacton swamp has been drained without a shot fired! Now for the Clacton plan..."
Liberal Democrat foreign affairs spokesman Tom Brake said: "This is yet another top Brexiteer leaving a sinking ship.
"It speaks volumes that UKIP's first elected MP is throwing his weight behind Theresa May, who has adopted UKIP's hard Brexit agenda to the letter."
When he quit UKIP last month, Mr Carswell said: "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."