A hard Brexit will lead the Conservatives to an election loss, George Osborne said.
The former Chancellor argued in favour of a soft Brexit and for modern, socially liberal values, highlighting his own rebellion in supporting gay adoption rights.
Mr Osborne, now the editor of the London Evening Standard, said a return to conservative social values, exemplified by the attitudes of arch-Brexiteers like Jacob Rees-Mogg, had already damaged the party and would do so again.
Addressing a Westminster correspondents’ lunch, he said: “If we present ourselves to the country as anti-modern, anti-immigrant, anti-urban, anti-metropolitan, then huge sections of the country will be anti-us.
“We saw that, frankly, at the last general election and we may see it in the London elections in a few months time.
“Change in a progressive country is constant and it is pointless resisting it. Instead, Conservatives should run with it and shape it.”
Mr Osborne said the 48% who voted to remain in the EU must be respected, with more than 60% of the public now thinking the UK Government is handling Brexit badly.
He also dismissed ideas of hard Brexit trade deals and deregulation as “fantasy”.
“Conservatives who say we should only listen to the 52% who voted leave should be told they are making a huge mistake,” he said.
“We will expose the false arguments and broken promises of the hard Brexiteers.”
After railing against extreme Conservatives, Mr Osborne warned the only reason Labour was not in a position to take over the reins was because of Jeremy Corbyn’s perceived extremism amongst older voters.
He said: “In my view for all his ability to connect to younger and more disillusioned voters, Jeremy Corbyn remains the biggest obstacle to Labour winning an election.
“If the party was led by a more moderate social democrat of even middling ability then they would now be 20 points ahead in the polls and on the cusp of power.
“The fact that a fringe far-left Labour leadership is even in contention for national office is, I’m afraid, a reflection of the state of the Conservative party.”