Boris Johnson and Jeremy Hunt have been warned they risk making the Conservatives unelectable if they take Britain out of the European Union without a deal.

New polling seen by The Independent suggests large swathes of traditional Tory voters have turned away from the party as its membership has become increasingly focused on Brexit, and that more will follow if the new leader opts for a no-deal outcome.

The survey suggests the opinions of the 160,000 Conservative members who will choose the new prime minister are increasingly out of kilter with the 11 million voters who backed the party in 2015 – the only election in 27 years when the Tories have won an overall majority in the Commons.

Some 30 per cent of 2015 Tory voters questioned by pollsters Survation said they would like the UK to remain in the EU, compared to 32 per cent who want no deal and 36 per cent who back leaving with an agreement with Brussels. The figures contrast sharply with recent polling suggesting that 83 per cent of current party members would support a no-deal leader.

And while 61 per cent of current members told the earlier YouGov survey they would be ready to accept “significant damage” to the UK economy as the price for Brexit, more than half (51 per cent) of the 2015 Tory voters said they were not prepared to suffer any financial loss whatsoever as a result of EU withdrawal, and just 8 per cent said they were willing to take a hit of £1,000 a year or more.

Cliffs of Dover lit up in Brexit protest Show all 5 1 /5 Cliffs of Dover lit up in Brexit protest Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this statement by Nigel Farage on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this statement by former Brexit secretary Dominic Raab on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message to the EU on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter Cliffs of Dover lit up in Brexit protest Campaign group Led By Donkeys projected this message on the Cliffs of Dover on the evening of April 4 @ByDonkeys / Twitter

The new polling, commissioned by the Tories Against Brexit group, was released as the two candidates prepared for the first national hustings of the leadership campaign in Birmingham on Saturday.

Having won the backing of MPs at Westminster, Mr Johnson and Mr Hunt must now court a constituency of Conservative Association members, more than half of whom are thought to have backed the Brexit Party in last month’s European elections and 46 per cent of whom told an earlier survey they would be happy for Nigel Farage to be leader.

The Leave.EU group claims to have recruited 25,000 pro-Brexit activists to the Conservative Party as part of a “Blue Wave” campaign launched by founder Arron Banks last September, with the aim of delivering the votes to replace Theresa May with a hardline Eurosceptic.

Mr Johnson has said he will take Britain out of the EU by 31 October with or without a deal, and while Mr Hunt has said he is ready to extend negotiations beyond Halloween, he has made clear he would accept a no-deal withdrawal rather than see Brexit halted.

Tories Against Brexit’s Simon Allison said that while the leadership candidates were concentrating on stemming the haemorrhage of votes to Mr Farage’s Brexit Party, they risk losing the moderate centre ground voters who have traditionally delivered Tory seats in London, Scotland and the leafy middle-class constituencies of southern England.

“It is the siren call of suicide,” Mr Allison told The Independent. “You are being lured onto the rocks by your members, but your members’ views are not the same as your voters’ views. There are no seats to be won from Ukip or the Brexit Party. By focusing on winning back Brexit Party voters, they are almost guaranteeing they can’t win an election.”

His analysis was echoed by Tory MP Antoinette Sandbach, who said: “The Conservative Party need to be clear – to win elections we have to be in the centre ground of politics.

“This is one of the reasons I supported Rory Stewart for leader, as it was clear he was able to reach into the middle ground of British politics and it is clear that the Conservative Party members need to consider very carefully who is best placed to do that out of the leadership candidates Jeremy Hunt and Boris Johnson.”

Antoinette Sandbach MP says the Conservative Party needs to reach for the centre ground (Rex)

Mr Allison pointed to evidence from the Survation survey suggesting just 43 per cent of the voters who put David Cameron in 10 Downing Street in 2015 would now back the Conservatives. While 26 per cent said they would now back the Brexit Party, 12 per cent had switched to more pro-European parties such as the Liberal Democrats, Greens or Labour.

And 26 per cent of the 2015 Tories said they would not be likely to vote for the party if it chose a leader committed to no deal. Analysis of the European elections has found that around four or five 2017 Tory voters switched to the Brexit Party for every one that went to a more pro-EU party. But the new polling suggests that defections among pre-referendum Tory voters are not all in one direction, with the split closer to two to one.

Boris Johnson says failing to leave by October 31 will be 'catastrophic' during leadership debate

Mr Allison said the 1998 decision to hand the choice of leader over to party members had left the Conservatives “in thrall to a group of self-selected activists whose views no longer represent those of our voters or our long-standing philosophy”. He said the party structures had been taken over in the past three years by people who are “not true Conservatives” and care only about leaving the EU.

“Any party whose members have diverged this far from their voter base is likely to have a short lifespan,” he said. “As the membership increasingly looks like the Brexit Party, the moderate voter base whose support is vital to win elections is following the slogan so loved by the isolationists – Leave means Leave.”