Boris Johnson was “one of the most damaging prime ministers in this country’s history”, according to the chairman of Nigel Farage’s Reform UK.
Zia Yusuf also said the disgraced ex-PM, found to have deliberately lied and lied again to parliament over Partygate, would not be welcome in his party.
He also accused Mr Johnson, one of the architects of Brexit, of betraying those who voted for it.
In an interview with BBC Radio 4’s Political Thinking podcast, he said: “History will judge Boris Johnson as one of the most damaging prime ministers in this country’s history.”
The rise in net migration during Mr Johnson’s time in power was “a total betrayal of everybody who voted for Brexit”, he said. “He took public spending close to Soviet Union spending. So there was nothing Conservative about him.”
He also branded the Tories an "extremely left-wing party" in government.
He did say that ex-home secretary Suella Braverman would be welcome in Reform UK, however, claiming she had been “excommunicated” and made a “pariah” by the Conservatives.
Mr Yusuf also claimed that his party, which is surging in the polls, could win hundreds of MPs at the next general election.
In a blow to Kemi Badenoch’s Tories, the latest poll suggests that as many as third of their voters from the 2024 election have switched to Reform UK.
According to the weekly tracker poll by Techne UK for The Independent, 33 per cent who said they voted Tory last year are now backing Mr Farage’s party.
And Reform UK are now joint top of the poll for the first time, putting it in line with YouGov poll earlier this week.
Mr Farage described the latest polls as “astonishing” just a day after he had launched a campaign to reverse a Labour decision to cancel local election contests for millions this May.
The crisis in support for the Conservative Party comes amid apparent splits at the top with shadow justice secretary and leadership contender runner-up Robert Jenrick refusing to rule out a deal with Reform, while a spokesperson for Ms Badenoch insisted it would not happen.
The Tory leader has also launched a hardline immigration policy to discourage low-paid workers from coming to the UK in an apparent bid to counter the threat from the right posed by Reform.
But the poll results will do nothing to stop the growing whispers about Ms Badenoch’s leadership within her party, a little over three months since she was elected.
