PRESSURE is growing on Theresa May again as Remain supporting Tory backbenchers are said to be giving their support to a bid to keep the UK in a customs union with the European Union after Brexit.

A cross-party amendment to the Trade Bill tabled by Conservative MP Anna Soubry calls on the UK Government to negotiate “a” customs union with the bloc.

Defeat for the Government on the proposed clause if it gets Labour support would be a major blow to the Prime Minister who has vowed to take the UK out of the customs union after Brexit.

Prominent names such as Heidi Allen, Bob Neil and Nicky Morgan have all said they would back the amendment when the bill returns to the Commons in May.

MPs Dominic Grieve and Stephen Hammond – who have also backed the amendment – even hinted they could vote against the Government and risk triggering a no-deal Brexit.

It marks the latest battle between pro-EU and anti-EU Tory MPs who are fighting over how closely aligned the UK will remain to the EU in terms of its regulatory framework including on issues such as workers rights and food safety standards.

Soubry told the PoliticsHome website: “Nobody wants to vote against their own government, but we have been put into a position before whereby we have had to do that to make sure things are done properly and in the best interests of Britain.”

Fellow Tory Remainer Allen said on Twitter: “My bosses are my constituents, and they voted remain.”

The amendment reads: “It shall be the objective of an appropriate authority to take all necessary steps to implement an international trade agreement which enables the UK to participate after exit day in a customs union with the EU.”

Grieve told the BBC he believed a “broad swathe of the Conservative party in parliament” backed the proposal.

Health Secretary Jeremy Hunt yesterday insisted the UK will not back a customs union with the EU despite the prospect of the humiliating Commons defeat.

Asked on Radio Four’s Today programme if the Government would change course, Hunt replied: “No, because if we were part of the customs union we wouldn’t be able to negotiate trade deals independently with other countries and we wouldn’t have full sovereign control of our destiny as a nation.”

Downing Street said: “We’re working towards getting a deal which we believe will work for all parts of the UK and deliver as frictionless a border as possible and tariff-free trade.”

The move comes as Jeremy Corbyn prepares to officially commit Labour to joining a customs union with the EU after Brexit.