Good that the splitters have gone, but this is a dangerous moment for the left, argues John Rees

Now that it has finally begun, we can assess the impact of a right-wing split from the Labour Party.

The split marks a failure for the right wing. Some of them have had to give up on the long guerrilla struggle to unseat Jeremy Corbyn and return the party to a Blairite, centrist path. Attempting to build a new centrist party was always Plan B for the right wing because it is much more difficult than restoring their ascendancy in the Labour Party.

Many on the Labour left will celebrate the departure of an internal opposition which has been relentless, unprincipled, and destructive in its attack on the leadership.

But, make no mistake, this is not the end of the struggle. And even the departure of Chuka Umunna and his friends will only be a partial victory if the left responds effectively. Let’s examine why.

Firstly, the new centrists will be held up as a constant argument that the Corbyn project is failing. Corbyn and his allies in the leadership have made so much of the argument that Labour is a broad church, and done much to limit attempts by rank-and-file Labour members at deselection, that any split is bound to be presented as a failure by the media and right-wing MPs.

Secondly, the new centrists will not simply go away. They will not return to their careers in business, or take up posts in the middle levels of the civil service, or spend more time with their families. The media will promote them relentlessly and on every possible opportunity.

Those that think that a small unrepresentative party with little electoral success cannot have a huge impact on an established party with considerable electoral representation should remind themselves of the effect that UKIP had on the Tory party. Its presence can be used to constantly drive the larger organisation in the direction of the departed minority.

Thirdly, by no means have all the right wing left. Those that remain will undoubtedly co-operate with those that have left. Their presence will be, if not properly dealt with, a knife at the throat of Jeremy Corbyn’s project.

The bluntest argument will simply be “do what we say, or we will leave and join the centrists”. So, the departure of some right-wing MPs, and the creation of a new centrist party, will not be the end of internal Labour Party struggles but the intensification of them.

What all this means is that the Labour left is faced with a choice: do you want a genuine left-wing workers’ party, or do you want to continue the losing battle to hold together a traditional Social Democratic party which contains right-wing, pro-capitalist, pro-imperialist, MPs?

What the creation of a new centre bloc shows is that the latter option is running out of road. It should prompt in the minds of Labour Party members some crucial questions. Why for instance are we endorsing the Trident missile system to placate a right wing who are clearly not interested in supporting a Corbyn-led Labour Party? Why did the NEC retreat over the definition of antisemitism when the people it was supposed to reassure are clearly set on the destructive course of undermining the Labour Party?

This should be the moment when the entire Labour left, including the leadership around Jeremy Corbyn, decisively strikeout to recreate Labour as a genuine socialist party. If they do not, then the right wing will use their new creation to continue the endless war of attrition against Jeremy Corbyn. And, the more the left attempts to hold them in the party by compromising with them, the more likely they are to succeed.