Clive Lewis, a key ally of Jeremy Corbyn, has resigned from Labour’s Shadow Cabinet after the leadership imposed a three-line whip on the Government’s Brexit bill.

In a statement Mr Lewis, who held the post as Shadow Business Secretary, said it was “with a heavy heart” he had decided to step down.

“When I became the MP for Norwich South, I promised my constituents I would be ‘Norwich’s voice in Westminster, not Westminster’s voice in Norwich’,” he said.

“I therefore cannot, in all good conscience, vote for something I believe will ultimately harm the city I have the honour to represent, love and call home.

It follows the Labour leader’s decision to impose a second three-line whip – the strongest possible instruction – on the third reading of the Government’s EU withdrawal bill on Wednesday. It is the legislation needed in order to trigger Article 50 of the Lisbon Treaty and begin the Brexit negotiations.

Mr Corbyn, the Labour leader, thanked his colleague for his work “which has underlined what an asset he is” to the Labour Party. “I understand the difficulties MPs representing constituencies which voted Remain have in relation to the European Union Withdrawal Bill. MPs have a duty to represent their constituents as well as their party,” he added.

“However, the Labour Party respects the outcome of the EU referendum, so we have asked all Labour MPs to vote for the Bill at its third reading tonight.

“We have been clear from the start that Labour will not frustrate the triggering of Article 50, which represents the start of the process for leaving the EU.

“Labour will use every opportunity to hold the government to account and protect jobs, rights and living standards at every stage of the negotiations. I wish Clive well and look forward to working with him in the future.”