Jo Stevens is first Labour Shadow Cabinet member to quit over Jeremy Corbyn's order to 'vote for Brexit'

‘I expect this to be the most important vote I will ever cast as an MP and for me it is a clear issue of principle and conscience’

Jo Stevens has resigned as Shadow Welsh Secretary (PA)

A member of Jeremy Corbyn’s Shadow Cabinet has quit her post, reigniting Labour’s bitter war over Brexit.

Jo Stevens, the Shadow Welsh Secretary, said leaving the EU would be “a terrible mistake” and she could not vote for it, as instructed by the Labour leader.

“I expect this to be the most important vote I will ever cast as an MP and for me it is a clear issue of principle and conscience,” she said.

The resignation came despite an olive branch offered by the leadership, after Mr Corbyn imposed a three-line whip to vote for the Article 50 Bill next week.

Diane Abbott, the Shadow Home Secretary, said Labour MPs might be allowed to oppose the Bill at a later stage if its amendments are thrown out.

However, the move failed to prevent the first loss of a Shadow Cabinet member since Mr Corbyn triumphed in last summer’s leadership battle.

In a letter to her leader, Ms Stevens said she was “a passionate European” who had voted to remain, as had most people in her city and constituency of Cardiff.

She said she accepted the referendum result and recognised that she could not block the passage of the EU withdrawal Bill.

But she added: “I believe that leaving is a terrible mistake and I cannot reconcile my overwhelming view that to endorse the step that will make exit inevitable is wrong.

“When I vote I will be representing my constituents, a great many of whom, including a great many Labour party members and voters, have strongly urged me to vote in this way.

“That is why, in Shadow Cabinet, I argued against the imposition of a three-line whip.”

The resignation follows that of a junior shadow minister, Tulip Siddiq, who resigned immediately after Mr Corbyn ordered his MPs into line.

Two whips, Jeff Smith and Thangam Debbonaire, have said they will defy Mr Corbyn, as has transport spokesman Daniel Zeichner.

Mr Zeichner told the Cambridge News” “They know my position and they understand exactly why I'm doing what I'm doing and it's for them to decide what to do next.”

Ms Abbott suggested the Labour rebels would escape punishment, saying there was “great sympathy” for MPs in pro-Remain constituencies.

And she defended Mr Corbyn's stand, telling the BBC: “You have to remember how this looks to people in post-industrial Britain, former mining areas, the North, the Midlands, South Wales.

“It would look as if elites were refusing to listen to them. It would be wrong.

“How could MPs vote for a referendum and then turn around and say 'It went the wrong way so we are ignoring it'?”

However, Ms Abbott also sparked further confusion about Labour’s position, saying: “Are we going to vote with the Tories come what may? This is a question of opening the process.

“We will seek to amend and, if we are not able to get any of our amendments through, clearly we will have to review our position.”

A Labour source confirmed to The Independent that the Shadow Cabinet decision was to support the Bill at second reading only, in a vote next Wednesday.

That will be followed by three days of line-by-line scrutiny in a Bill committee, at which Labour will attempt to shape the Brexit process.

Most important, it is demanding a “meaningful vote” in Parliament on the final Brexit deal – early enough for Ms May to seek better terms if hers are rejected by MPs.

The source insisted there was no question of Labour MPs being told to vote against Article 50 Bill – even if all the amendments fall – but the whip could be removed.

Clive Lewis, the Shadow Business Secretary, has said he will vote for the Bill on second reading, but could withdraw support in the final stages.