Mr Farron claimed Theresa May had “hung out to dry” business through her decision to take Britain out out of the European single market and alienated Tory MPs who had signed up to David Cameron’s ‘compassionate Conservatism’ with her approach to immigration and child refugees.
He accused the Prime Minister of sharing the politics of US President Donald Trump, Russian President Vladimir Putin and French Front Nationale leader Marine Le Pen.
The Lib Dem leader said control of the Conservatives had been seized by “May’s Momentum”, a reference to the campaign group which supported Jeremy Corbyn becoming Labour leader.
He said: “The Hard Brexiteers. The anti-free trade protectionists. The shrink-the-state extremists. The anti-immigrant, anti-refugee, anti-international aid zealots.
“It’s their party now – and it’s hard to be sure whether Theresa May is their leader or their captive.”
Mr Farron told delegates at the Lib Dem Spring conference in York the Conservatives’ business backers had been “sold a free market, internationalist, pro-business party but what you’ve got is protectionism, nationalism, economic vandalism”.
He acknowledged voters had chosen Britain should leave the EU in last year’s referendum but argued the decision to leave the single market was down to the Prime Minister.
In an appeal to Tory donors he said: “If you want to stop the Conservative Government taking our country out of the single market without any mandate to do so, you don’t have long to do it, and you don’t have time to do it subtly.
“But you can help rescue Britain’s economy and protect your business.
“You need to dump the Tories and back the Liberal Democrats right now.”
In the aftermath of the EU referemdum and Labour’s uncertain position on the issue, the Lib Dems have framed themselves as the only credible opposition to tbe Conservatives.
This speech marked a change in tone as Mr Farron made a determined pitch for pro-Remain Conservative MPs and voters attracted to the party under Mr Cameron.
Mr Farron said Tory MPs elected at the last two General Elections were “attracted by a new era of Compassionate Conservatism” but that party had now “gone”.
Referring to the Richmond Park by-election last year, Mr Farron said told moderate Conservative MPs: “You are now the supporters of a Government that is as anti-business as Jeremy Corbyn.
“You are now the cheerleaders of a government that is an anti-refugees as Nigel Farage.
“You are now backing an agenda that is the opposite of what you signed up for.
“And you know it’s wrong, so for pity’s sake, have some self-respect. Defect or resign.
“If you don’t then when the next election comes we will do to you what we did to Zac Goldsmith.”
The Lib Dem leader said his party was now engaged in a “fight for Britain’s future” and claimed the party could win enough seats at the next General Election to deny Theresa May a majority.
“It is still possible for the British people to stop a Hard Brexit.
“It is still possible for the British people to keep us in the Single Market.
“And if they want, it is still possible for the British people to change their minds and remain in the European Union,” he said.
Mr Farron told the conference the Lib Dems “can be more than just the real opposition. We can be an alternative government.”