Nigel Farage has announced he is quitting Ukip.
The former leader said he had made the decision because he is uncomfortable with the direction Ukip has taken in recent months.
Mr Farage had previously called for Ukip leader Gerard Batten to be ousted after he appointed English Defence League (EDL) founder Tommy Robinson as an adviser.
Writing in the Daily Telegraph, Mr Farage said: “And so, with a heavy heart, and after all my years of devotion to the party, I am leaving Ukip today.
“There is a huge space for a Brexit party in British politics, but it won’t be filled by Ukip.”
Mr Farage insisted Ukip had been successful in the past because it had a policy of “excluding extremists”.
The ex-leader said Ukip was becoming a party of “street activism”.
Mr Farage said: “Under my leadership of Ukip, the party banned former members of the BNP and EDL from joining.
“Many accusations of racism and extremism were thrown at us, but I strongly maintain they were untrue.
“Under Gerard Batten’s leadership, however, the party’s direction has changed fundamentally.
“Analysis of weekly local council by-elections up and down the country shows that Ukip now fields very few candidates.
“Worse still, many of our very best organisers and activists on the ground have resigned their positions.
“This means we no longer have a professional campaigning team.
“The party of elections is quickly becoming a party of street activism, with our members being urged to attend marches rather than taking the fight to the ballot box.
“The great irony of this change in approach is that it is happening at a time of maximum electoral opportunity for Ukip.
“With the Conservative and Labour parties having openly broken both their referendum and general election promises, Ukip should be riding high in the polls.
“With regret, however, I must admit that I now do not believe it will do so again.
“Mr Batten’s obsession with Stephen Yaxley-Lennon – to use Tommy Robinson’s real name – and fixation with the issue of Islam makes Ukip unrecognisable to many of us.
“While Robinson may hold an appeal to some members of society who feel they are disenfranchised, I believe he is entirely unsuitable to be involved in any political party.”
Mr Batten tweeted: “I hear that Nigel Farage has resigned from UKIP.
“Nigel & I were founder members of UKIP in 1993. I have always given him full credit for his work in UKIP bringing about and winning the Referendum. However, I feel that he left UKIP in spirit after the Referendum.”
And Ukip deputy leader Mike Hookem was scathing about Mr Farage.
The Yorkshire and North Lincolnshire MEP said: “Nigel has made some catastrophic political decisions recently and he knows his star is fading fast among the membership and the public alike.
“The loss of Nigel as a supporter will have an impact in sentimental terms, but in practical terms, he is no significant loss.”
Mr Hookem added that Mr Farage would be a hypocrite if he did not quit as an MEP.
“What I really want to know is when Farage intends to resign his seat as an MEP?
“In 2014, Nigel demanded all incoming Ukip MEPs sign a letter stating they would hand their seat back to the party if we were to leave. We all signed.
“Nigel even went as far as demanding Diane James hand back her seat on leaving the party in 2016.
“Therefore, he would be an utter hypocrite to keep his own seat on leaving the party, as have the others who have left.”