Jeremy Hunt has warned Theresa May that signing up to a customs union with Labour to break the Brexit impasse would alienate Tory MPs.

The foreign secretary said agreeing to Labour's foremost demand could backfire for the prime minister, as the government "would lose more Conservative MPs [it] would than gain Labour MPs".

It comes as speculation mounts over a possible breakthrough in the cross-party talks, which were described as "positive" and "productive" by David Lidington, the de-facto deputy prime minister.

Mr Hunt, who is seen as contender to succeed Ms May, made the comments on a week-long trip to Africa where he is seeking to extol the virtues of post-Brexit trade.

He told BBC Radio 4's Today programme: "If we were proposing, which I very much hope we don't, to sign up to the customs union, then I think there is a risk that you would lose more Conservative MPs than you would gain Labour MPs.

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"If, on the other hand, it was something different, then the result could be different as well."

Mr Hunt insisted there was a "great sense of urgency" in the negotiations with Labour but his comments will cast doubt on the prospect of success.

He also sought to ramp up pressure on the Labour leadership, saying: "Labour voters want this result remember, they don't want Brexit paralysis affecting their jobs and businesses.

"There are many Leave voters in Labour seats who voted Labour, they have Labour MPs and they want to see the party honour its own commitment to abide by the referendum result."

Both parties will be punished at the ballot boxes in the upcoming local and European elections if Brexit is not delivered, he added.

Mr Hunt also dodged questions about whether Theresa May should quit, saying a change of prime minister "doesn't actually change the parliamentary arithmetic".

It comes as grassroots Tories told the prime minister she could face a challenge to her leadership at an unprecedented summit in June.

Local constituency chairman have reached enough support to force an emergency general meeting to discuss Ms May’s premiership and her strategy on leaving the European Union.

The prime minister was reportedly notified of the news by the head of the National Conservative Convention, Andrew Sharpe, on Monday, after more than 10 per cent of local parties signed a petition calling for her to go.

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Meanwhile, Labour was embroiled in an internal row over whether to commit to a Final Say referendum on any Brexit deal.