Rachael Maskell and Dawn Butler have resigned from Labour’s Shadow Cabinet following Jeremy Corbyn’s decision to impose a three-line whip and force his MPs to vote for invoking Article 50.

Their decision comes less than an hour ahead of a crucial vote on the second reading in the Commons of the Government’s EU Withdrawal Bill – the legislation needed to trigger Article 50 of the Lisbon Treaty.

The Independent understands Ms Maskell, the Shadow Environment, Food and Rural Affairs Secretary, made her decision after meeting with constituents at two public meetings to hear their concerns over Article 50. The majority lobbied her to defy the three-line whip imposed by the Labour leadership last week.

Ms Maskell, who remained loyal to the Labour leader during an attempted coup in the summer of 2016, is the MP for York Central – an area the voted overwhelmingly to remain inside the European Union at the referendum in June last year.

In a statement, Mr Corbyn said: “I would like to thank Dawn and Rachael for their work in the shadow cabinet. They are great assets to the Labour Party and to our movement.

“MPs have a duty to represent their constituents as well as their party, and I understand the difficulties that MPs for constituencies which voted Remain have in relation to the European Union withdrawal Bill.

“However, it is right that the Labour Party respects the outcome of the referendum on leaving the European Union. We have said all along that Labour will not frustrate the triggering of Article 50 and to that end we are asking all MPs to vote for the Bill at its second reading tonight.

Her decision to stand down comes after Jo Stevens, the Shadow Welsh Secretary, became the first member of the Shadow Cabinet to stand aside, saying she could not reconcile herself to vote to invoke Article 50.

It is expected that dozens of Labour MPs could defy the three-line whip – especially those in metropolitan constituencies that voted overwhelmingly to remain in the EU. Frontbenchers Catherine West, Tulip Sidiq and Daniel Zeichner have all said they would vote against the Government’s Bill.

Rupa Huq, the Labour MP for Ealing Central and shadow home office minister, told The Independent she is also prepared to vote against triggering Article 50 and that her position has been clear since the referendum. Asked whether she was expecting any consequences, she replied: “We’ll cross that bridge when we come to it”.

In an extraordinary situation, three out of Labour’s 12 whips, responsible for keeping MPs in line, have vowed publicly to defy the whip and vote against the triggering of Article 50. These include Jeff Smith, the MP for Manchester Withington, Thangam Debbonaire, the MP for Bristol West, and Vicky Foxcroft, the MP for Lewisham.

The Independent understands that the positions of members of the Shadow Cabinet and frontbench, who defy the three-line, will be considered untenable after the vote later this week. Asked on ITV’s Peston on Sunday whether his MPs would have to resign if they voted against invoking Article 50, Mr Corbyn replied: “As of now, nobody has voted on anything. There was no need for anyone to resign at this stage.

“It’s obviously impossible to carry on being in the Shadow Cabinet if you actually vote against a decision made after a very frank and long discussion of the Shadow Cabinet earlier this week.

“However, we are a party with massive talents… I expect and assume, and I think everyone would agree that every Labour MP is going to vote for the amendments that Keir Starmer and I have put before the House this week”.

Mr Corbyn has made clear for several months that Labour would not seek to frustrate the will of the people and vote with the Government in invoking Article 50 of the Lisbon Treaty.

Owen Smith, the former Labour leadership candidate, told the BBC Radio 4 Today programme earlier on Tuesday he would also defy Mr Corbyn’s orders and vote against Article 50, as he accused the Prime Minister of “dissembling” on the issue.