The shadow secretary for Wales, Jo Stevens, has resigned from her post, saying she could not reconcile herself to voting to trigger article 50 as she still believed leaving the EU would be “a terrible mistake”.

In her letter to the Labour leader, Jeremy Corbyn, Stevens said she was “a passionate European” who had voted to remain, as had a significant majority of her city and constituency of Cardiff.

The MP said she accepted the referendum result and recognised that she could not block the passage of the EU withdrawal bill and that exiting the EU was inevitable. “But 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,” she wrote.

“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. 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.”

Stevens is the first shadow cabinet member to resign over the issue, after Corbyn said he would impose a three-line whip to vote in favour of the government’s EU withdrawal bill.

Tulip Siddiq resigned from frontbench on Thursday. Photograph: Nicola Tree/Getty Images

Tulip Siddiq resigned as shadow early years minister on Thursday, saying she intended to vote in line with her strongly pro-remain constituents in Hampstead and Kilburn.

Stevens was elected in 2015, beating the Lib Dem incumbent Jenny Willott with a majority of 4,981. Though Wales voted overall to leave the EU, Cardiff was pro-remain, with 60% of people voting to stay in.

Stevens previously expressed concern about the impact of leaving the EU on her brief, with 68% of Welsh exports going to the EU.

On the left of the party, Stevens was one of 40 MPs who refused to back a no-confidence motion in Corbyn after the EU referendum, but she later endorsed his leadership rival Owen Smith. She was previously shadow justice minister but was promoted to the shadow cabinet and given the Wales portfolio after Corbyn’s reelection in October.

Stevens was among those who argued that MPs should not be compelled to vote for the government’s bill, along with the shadow business secretary, Clive Lewis. Lewis has since said he will vote in favour of the bill on second reading, but hinted he could be prepared to withdraw support in the final stages.

Two Labour whips, Jeff Smith and Thangam Debbonaire, have also said they will not vote for the bill, as have their fellow shadow ministers Daniel Zeichner and Catherine West, though it is not yet clear if they will be forced to resign in order to do so.

In her letter, which has been emailed to local party members, Stevens said Theresa May was pursuing “a brutal exit with all the damage that will cause to the people and communities we represent”.

Stevens said she believed Corbyn, who defied the Labour whip on issues of conscience hundreds of times during the Tony Blair and Gordon Brown years, would understand her strength of feeling. “I must follow my principles and my conscience, even where that conflicts with the party’s whip in parliament,” she wrote.

“It is with deep regret that this inevitably means I must resign from the shadow cabinet. It has been an honour and a privilege to serve as your shadow secretary of state for Wales, the country where I was born, bred, work and live.

“In carrying out that role, it reinforced even more strongly to me what Wales will lose from exiting the EU without the guarantees that are needed and without a seat at the negotiating table for the people of Wales. We are net beneficiaries of EU funding. Over two-thirds of our exports are to the EU. It is a lifeline to our manufacturing industry in steel, automotive and aerospace as well as to our farming and food production sector. I do not believe that we can rely on a Conservative government to protect Wales.”

Corbyn and Thangam Debbonaire, who has said she will not vote for triggering article 50. Photograph: Chapman/LNP/Rex/Shutterstock

Stevens said she was not seeking to sow division in the party. “Throughout my period on the frontbench I have always sought to promote unity across our party and I wish you, my successor and the whole of the shadow cabinet the very best in leading our party through this most critical period,” she said in her letter to Corbyn.

Earlier on Friday, the shadow home secretary, Diane Abbott, whose constituents in Hackney voted overwhelmingly to remain in the EU, defended Corbyn’s stance. “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,” she told BBC Radio 4’s Today programme.



“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?”

Corbyn has said he understands the pressures facing his MPs but urged the party to unite, saying: “Labour is in the almost unique position of having MPs representing constituencies in both directions, and very strongly in both directions.

“I say to everyone: unite around the important issues of jobs, security, economy, rights, justice, those issues, and we will frame that relationship with Europe in the future outside the EU, but in concert with friends, whether those countries are outside or inside the EU.”