At the end of last week Frank Field and Kate Hoey, two pro-Brexit Labour MPs, lost a no-confidence vote in their local constituency parties. Members accused the pair of rescuing the government, along with two other pro-Brexit Labour colleagues, from a Commons defeat on an amendment to the Trade Bill which had it lost, could have set in motion the collapse of May’s government and a possible general election. The government won by a majority of just six votes.

Laura Parke, leader of Momentum, began the backlash against the Brexit backing MPs, calling for them to be de-selected.

So far, moderate Labour MPs have remained strikingly silent on the issue. Most would be inclined to support the move against their pro-Brexit colleagues, with the moderate wing of the Labour party being one of the groups most viscerally opposed to Britain’s departure from the European Union.

However, a failure to defend the right of MPs to vote in line with their principles, and to uphold the Labour party as a broad church containing a range of opinions, would set a dangerous precedent which could come back to haunt anti-Corbyn MPs.

Frank Field is one of the most principled and effective members of parliament in recent history. His campaigning on poverty, hunger and slavery has improved the lives of many of the most vulnerable people in Britain.

However, he is also one the remnants of a dying tradition on the Left, which combines a social democratic outlook with social and cultural conservatism. He is sceptical about mass migration and a life-long Eurosceptic. In this, he represents the views of the majority of his constituents, who voted to leave. Someone in parliament must speak for the millions of Labour voters who defied the party’s consensus on EU membership two years ago.

What’s more, his support for Brexit is in keeping with a rich tradition within the Labour movement, which is not confined to the Bennite Left. Clement Attlee, Hugh Gaitskell and Barbara Castle, great figures in the history of the Labour party, all opposed British integration with Europe.

More pressingly for the moderates, if Momentum activists are successful in deselecting pro-Brexit MPs, an almighty purge will ensue, engulfing any MP deemed insufficiently loyal to the party leadership. Fervently anti-Brexit Blairites like Chuka Umunna may well be top of the list. They should have the foresight to transcend the bitter Brexit divide and come to the defence of their pro-Leave colleagues to prevent the Parliamentary Labour Party from becoming a Corbynite monolith.