The priority for the nation over the next six months is to get Brexit right – preferably by holding a referendum to give the people a final say over the terms on which we leave. Other things are important, such as the Budget, but one thing that is a distraction is the campaign in the Labour Party to force some of its MPs out of parliament at the next election.

Chuka Umunna, who is one of the Labour MPs targeted for deselection and who leads the campaign for a final say referendum, made a powerful speech today making this twin argument.

Mr Umunna attracted some attention for the phrase, “call off the dogs”, addressed to Jeremy Corbyn, the Labour leader. It is worth quoting that passage in full: “My message to our leadership: it is within your power to stop this so call off the dogs and get on with what my constituency, one of the most diverse communities in the nation, demands we do – without equivocation, fight this Tory Brexit. That is where all our efforts should be.”

He is absolutely right. Mr Corbyn, who promised a kinder, gentler politics, has allowed his supporters to attack other Labour members on social media in the most vicious terms. Mr Corbyn has occasionally issued a general plea for civility, like a teacher who has lost control of the class. But if he really wanted to stop it, he would condemn specific instances from high-profile supporters and ask for them to be deleted.

Some of his supporters have attacked Jewish MPs and posted antisemitic comments in his name, prompting at most half-hearted and tardy disciplinary action. And now Momentum, the group set up to campaign for Mr Corbyn in the 2015 leadership election, is backing rule changes at this month’s Labour conference to make it easier to deselect Labour MPs.

We suspect that Mr Corbyn knows that this is not in his interest. He does not want local Labour parties torn apart by deselection battles over the next three and a half years. Of course he would like more Labour MPs to be more supportive, but not at the cost of protracted infighting and bitterness. After all, he managed to fight the last election remarkably well without the support of most of his MPs.

Mr Corbyn must know, too, that the best way of maintaining some semblance of unity in his parliamentary party is to oppose a “Tory Brexit” with skill and vigour. Keir Starmer, the shadow Brexit secretary, has positioned the party adroitly so that it is poised to strike during the final stages of the Brussels negotiations.

The opposition can try to push the government into a deal that is better for Britain by aligning us as closely as possible with the EU single market, and has wisely held the option of a new referendum in reserve.