Nigel Farage and Ukip donor Arron Banks have accused the Conservatives of stealing Ukip’s clothes, following Theresa May’s new hard-line approach to immigration.
Both Mr Banks and Mr Farage, who returned as interim Ukip leader following Diane James’s resignation, claimed it showed they had shifted centre-ground politics to the right.
It came as the favourite to be the party's next leader Steven Woolfe revealed he had been tempted to defect to the Tories under Ms May.
The strict controls on immigration, and in particular a plan to make companies publish the proportion of their workforce which is foreign, have been slammed by Labour and the Liberal Democrats.
Speaking to Channel 4 News, Mr Farage called Ms May's conference speech "remarkable", before adding: "It made you realise the extent to which Ukip hadn't just pushed for, gained and helped to win a referendum, but actually we've changed the centre of gravity of British politics.
"Virtually everything she said in that speech are things I've said to the Ukip conference over the last five or six years."
On BBC Newsnight, Mr Banks made similar comments, saying: "If you looked at Theresa May's speech today, it was really Nigel Farage giving a speech.
"It's all of the policies he's been condemned for, for a very long time.
"She’s basically today, rebranded the Conservative Party Ukip."
Mr Banks, the major Ukip donor, went on to say that Mr Woolfe "is the one candidate who can do it" when it comes to replacing Mr Farage as leader.
MEP Mr Woolfe admitted he had considered defecting to the Tories, before deciding to stick with Ukip.
In a statement, Mr Woolfe disclosed he had been "enthused" by Theresa May's start to her premiership, but in the end concluded only Ukip could be relied upon to deliver on Brexit.
He said: "Her support of new grammar schools, her words on social mobility and the growing evidence that she is committed to a clean Brexit prompted me, as it did many of my friends and colleagues, to wonder whether our future was within her new Conservative Party.
"However, having watched the Prime Minister's speech on Sunday I came to the conclusion that only a strong Ukip can guarantee Brexit is delivered in full and only our party can stand up for the communities of the Midlands and the North."
Mr Woolfe was barred from standing in the last leadership contest after submitting his nomination papers 17 minutes late.
Nigel Farage's ex-aide Raheem Kassam is also putting himself forward for the pending leadership contest.
The party's ruling executive committee will now meet on October 17 to agree a timetable for an election to find a permanent replacement for Ms James.
In her resignation statement released late on Tuesday, she said she was standing down for "personal and professional" reasons, citing a lack of support among the party's MEPs and officials.
It is thought that her husband's ill health may also have played a role, while Mr Farage pointed to an incident at London's Waterloo Station in which she was verbally abused and spat at.
Mr Farage said he expects a new leader to be appointed before the end of November.
Former deputy leader Paul Nuttall, former deputy chairwoman Suzanne Evans, who has just returned to Ukip after a suspension, and Lisa Duffy, who came second to Ms James in the last leadership contest, are all said to be considering a bid.
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