TIG has already rattled Corbyn. Now, the battle is really on.

Perhaps the Independent Group – or the party into which it will inevitably morph – will achieve little electorally. Critics are quick to point to the experience of the SDP in the 1980s and the crushing nature of the UK’s first-past-the-post electoral system.

But those who obsess over the chances of a breakthrough in a general election are missing the point entirely.

The very emergence of TIG is the single best thing to happen to British politics in some years.

The breakaway faction offers a potential choice to voters that goes beyond hard-left vision of Jeremy Corbyn and the laissez-faire madness championed by the Tories.

It exposes the vacuous claim of the far left that ‘centrism’ is now dead and has no natural constituency.

It shakes up the arithmetic in Parliament and presents some new possibilities in the endless and painful debate over Brexit. (Indeed, in recent days John McDonnell and others have signalled that Labour might be more inclined to embrace a second referendum. The Shadow Chancellor knows that more concessions are needed to prevent further walk-outs.)

So without forming a political party proper and without contesting any public election, the Independent Group has already shaken up British politics.

For me, as a former Labour parliamentary candidate, the most exhilarating thing about TIG is the fact that people have finally called Corbyn’s bluff. The veteran leftist believed that he could push and push and push with no consequences. His online supporters – a motley collection of cranks, bullies, trolls and Trots – have been given free rein to snipe and intimidate.

Now, at last, they’re on the defensive.

When TIG launched, its members not only attacked Corbyn over Brexit and the anti-semitism crisis. They also made a point of exposing his dangerous foreign policy and hopeless incompetence. These are things that need to be right out in the open. And, now, free of the shackles of party discipline, these parliamentarians can actually speak their minds.

The reaction of some Corbynistas is to pretend that TIG is an irrelevance, although polls in recent days suggest otherwise. The majority, however, lash out. They denounce the ‘scabs’ and ‘traitors’ who have left the movement and prioritise campaigns to oust them from their seats.

Let the hard left huff and puff. Because it’s their house that is going get blown down.

But what of the likes of Emily Thornberry? The Shadow Foreign Secretary joins the Jezuits in vitriolic attacks on her former colleagues. She – along with others, such as Barry Gardiner and Baroness Chakrabarti – seem determined to nail their colours firmly to the Corbyn mast, no matter what. But they need to realise that when the ship hits the shore, no one will be interested in rescuing the survivors.

Tom Watson, as ever, teeters. The Labour Deputy Leader expresses sorrow in video messages and wrings his hands at the news of the breakaway. But what does he actually do? Every day he has spent in office has been a day facilitating Corbyn, by propping up the regime and giving it undeserved credibility.

The challenge to the remaining moderates in Labour is this: do you stick with the Momentum project while it self-destructs? Or do you play a part in finishing the disastrous Corbyn experiment and breathing new life into British democracy?