BIRKENHEAD MP Frank Field was one of four Labour rebels who helped Theresa May win a crucial Brexit vote earlier this week.

The Prime Minister was saved from a humiliating reverse by the votes of four Labour Brexiteers – and one currently sitting as an independent – who backed the Government in the crucial division.

Labour's Mr Field, Kate Hoey, John Mann and Graham Stringer – along with independent Kelvin Hopkins – voted with the Government.

All of them had previously backed the medicine regulation amendment, except for Ms Hoey who did not vote.

But 12 Conservatives broke ranks to back the customs union measure, even though it is understood that Tory whips told would-be rebels that there would be a confidence vote that evening if it passed.

Mrs May went down to defeat on a separate amendment to her flagship Trade Bill, which will require her to seek continued UK participation in the EU’s system for regulation of medicines after Brexit.

In dramatic scenes in the House of Commons, ministers made last-ditch efforts to stave off defeat by offering to introduce amendments in the House of Lords which would deal with 'the essence' of rebel Tories’ concerns over future arrangements.

But despite the rebels’ rejection of this overture, Mrs May emerged triumphant by a margin of just six votes, as the Commons rejected the key amendment by 307-301.

Former minister Guto Bebb, who quit his defence brief on Monday in protest at Government concessions to hard Brexit Tories, was among 12 Conservative MPs who rebelled over the customs union plan.

He was joined by Heidi Allen, Kenneth Clarke, Jonathan Djanogly, Dominic Grieve, Stephen Hammond, Phillip Lee, Nicky Morgan, Bob Neill, Antoinette Sandbach, Anna Soubry and Sarah Wollaston.

A senior minister told the Press Association it was “extraordinary that we lost the vote that didn’t matter and won the one that did."

But the minister added: “I don’t know where we go from here.”

The amendment would have forced the Government to adopt a negotiating objective of seeking to keep the UK in “a customs union” with the EU after Brexit, unless it has managed to negotiate a “frictionless free trade area for goods” by January 21 next year.

Downing Street insisted that this would have breached Mrs May’s red line, set out in last year’s Lancaster House speech and enshrined in the Chequers Cabinet agreement, to take Britain out of the customs union.