BITTER rifts have emerged in the Conservative leadership battle amid a growing campaign to ensure "anyone but Boris" becomes the next Prime Minister.

Remain campaigners accused the former London mayor of making contradictory pledges to voters that cannot possibly be delivered.

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There was fury among many Tory MPs as prominent Leave campaigners walked back from a series of promises within hours of the Brexit result.

These included claims of an extra £350 million a week that could be spent on the NHS and an end to the automatic right of EU citizens to come to the UK.

Philip Hammond, the foreign secretary, said that Mr Johnson and other Brexiteers had to explain to voters how they they would reconcile “mutually incompatible” pledges made during the referendum campaign.

Mr Hammond told ITV’s Peston on Sunday: “The key Leave campaigners made contradictory promises to the British people.”

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He added: “Boris is one of those.”

“Now they will have to resolve that by explaining how they will balance the trade-offs… between the different things they promised which are mutually incompatible. That will be hugely disappointing to a lot of people in this country who voted leave.

"How that trade-off is made is the key question now for the future prosperity of this country”.

Mr Johnson has also been attacked for suggesting to MPs that he would call a snap general election if he won the leadership.

READ MORE: The Midge: Alex Salmond says Brexit will break up UK, Nicola Sturgeon believes Scottish Parliament could veto move, Merkel in crisis meeting

One Tory MP described that idea as “utter madness”.

Meanwhile, other Remain campaigners demanded a new leader who could unite the party.

One Tory cabinet minister urged Mr Johnson and the Home Secretary Theresa May, seen as one of his most serious rivals, to run on a joint ticket to unite the party.

International Development Secretary Justine Greening urged the two to strike a deal in a bid to avoid a potentially damaging leadership contest.

A "strong Conservative government" should have Mr Johnson at its centre as a result of the Brexit voter, she said.

But Mrs May would be crucial to issues on migration and freedom of movement, she added.

Writing on the Conservative Home website Ms Greening, who campaigned for the UK to stay in the EU, said: "A leadership contest now is not in the interests of our country. It will mean our party focuses inward - at the very time our country most needs us to focus outward.”

She called for a agreement between Mr Johnson and Mrs May where “under one or the other” they could form a united leadership.

But former leader Iain Duncan Smith said that the next Tory Prime Minister must come from the Leave camp.

His comments potentially rule out Mrs May, who campaigned to staying the EU, although she was seen as keeping a low-profile in the campaign.

While Mr Johnson and Mrs May are seen as the two leading candidates they could be joined by others.

Former defence secretary Liam Fox said yesterday that he was "thinking about" standing.

Mr Cameron fired the starting gun on the race when he resigned on Friday morning.

At the time he said that he believed that his replacement should be in place by the party’s annual conference in October.

Any delay in choosing a new leader could also delay the UK’s exit from the EU.

Mr Cameron did not trigger that process on Friday, saying that task would be up to his successor.

Others have suggested that all the potential runners and riders should be allowed to campaign at the conference, before the final two-person shortlist is decided by MPs afterwards.

Party members will have the final say.

A poll by the Mail on Sunday suggests that in a head to head Mrs May could pip Mr Johnson by 53 per cent to 47 per cent.

Others that could throw their hats in the ring include the work and pensions secretary, Stephen Crabb.

He wrote yesterday about the disenchantment felt in poorer areas with “a political class in Westminster which now looks the same, dresses the same way, and speaks the same strange language”.