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Tory soft-Brexit backers today demanded Theresa May give ground on a customs union in return for avoiding a series of defeats in the Commons.

A senior Remain campaigner upped the pressure by calling for “further concessions” on the issue as the price of avoiding a major rebellion.

Conservative MP Sarah Wollaston said she was also “minded” to defy the whips by backing a Lords amendment on giving Parliament a meaningful vote on an exit deal.

“I think what matters most here is that all parliamentarians actually focus on the issue at hand.

"This isn’t about narrow party politics,” she told BBC Radio 4’s Today programme. Senior supporters of a soft Brexit told the Standard they believed the Government would offer an olive branch when Mrs May makes an appeal for unity at a meeting with MPs tonight.

Both sides agree it could be counterproductive for the Prime Minister to be defeated on a key issue before this month’s EU summit, starting on June 28, where she will be attempting to negotiate trade rights.

However, this week’s votes could reveal how vulnerable the Government is to being defeated if Parliament decides to assert its authority later this summer.

The key votes are:

A Lords amendment requiring a government statement on negotiations for a customs union deal. There is potential risk of a government defeat.

An amendment giving Parliament the power to take over negotiations if MPs reject Mrs May’s Brexit deal in October. Rebel Tories are less united on this, making it a low risk of defeat.

A vote on staying in the European Economic Area, including free trade and free movement of people. Jeremy Corbyn has let ministers off the hook through the leadership’s stance that the party should abstain — but the vote may reveal the strength of Tory and Labour rebels.

A senior Tory rebel leader told the Standard: “Conservatives are coming together behind the need to do a deal, leaving the ERG [Jacob Rees-Mogg’s anti-EU European Research Group] isolated.” Mr Rees-Mogg told LBC radio: “I think there will be some unity this week, it won’t be perfect but it ought to be enough to get the bill through and to reinforce the strength of Theresa May’s position.”

In what is likely to be a highly charged appearance before the backbench 1922 Committee tonight, the Prime Minister will remind her MPs they have a duty to deliver on the referendum vote to leave the EU.

“The message we send to the country through our votes this week is important,” she will say. “We must be clear that we are united as a party in our determination to deliver on the decision made by the British people.

“They want us to deliver on Brexit and build a brighter future for Britain.”