Seven Labour MPs: Chris Leslie, Luciana Berger, Ann Coffey, Chuka Umunna, Mike Gapes, Angela Smith and Gavin Shuker have left the Labour Party. They will sit as a new Independent Group of MPs while planning their next steps, just as the Gang of Four – the four Labour ministers who broke away to form the SDP in 1981 – left in January but didn’t ultimately form a political party until March.

For all seven, the decision to leave was essentially made long ago. One of their number described themselves as “emotionally disconnected” from the Labour Party as far back as the summer of 2018, another has long been freely saying that “the Labour Party no longer exists”, and all have before now made statements on the record that were impossible to reconcile with continuing membership of the Labour party. Luciana Berger, who spoke first at County Hall, from where I write today’s email, spoke of becoming “embarrassed” by the state of the Labour Party, whose values of equality have been “undermined and attacked”. She spoke of “leaving a culture of bullying, bigotry and intimidation”.

For many involved with the breakaway, relief, tinged with sadness, is the overwhelming emotion at leaving.

But will they succeed even in equalling the successes of the Gang of Four, who surged in the polls, eventually recruited 35 MPs to their banner, fought Labour to a near draw in the popular vote but were crushed by First Past the Post? Well, rather like the consequences of the French Revolution, it is too early to say, but there are some variables to consider.

The first is that we don’t know when the next election will be. The Gang of Four had the advantage of a Conservative government with a stable parliamentary majority and the knowledge that the parliament would run until at least 1983. This parliament might not make it until the end of March.

What we also don’t know is what the Labour Party will do. One reason why the SDP’s ranks swelled from four to 21 to ultimately 35 MPs, is because while some MPs left due to their principled opposition to the party’s direction, others left under threat of deselection. It’s a tricky dilemma for the Labour leadership: if they are to be an effective government they need to remake the Parliamentary Labour Party. But if they remake the Parliamentary Labour Party they may give swell this new grouping’s size well beyond seven.

Then there’s the question of the party’s platform. All have been deeply opposed to the Labour leadership’s position on a swathe of issues, from its handling of anti-Semitism in party ranks to economic policy, to foreign policy, security issues and, of course, the question of how to handle Brexit.

While there is a relative degree of ideological kinship here they don’t all sing from the same hymnbook. The strength of one reason to split over another varies from member to member, and just as the SDP eventually collapsed into infighting about whether they were seeking to recreate the Labour Party of Hugh Gaitskell or seeking to form a new centrist force, it is wholly possible that this grouping will likewise struggle to decide if it is offering “Labour minus anti-Semitism” or “the Liberal Democrats plus political viability”. Gavin Shuker – who, behind the scenes, several of those making the jump today have credited with persuading them to make the leap – gave a list of values that could easily apply to either definition, which may be part of its potential political appeal but could also be what costs it.

They’ve chosen a good week with not much else going on, in which plenty of attention will be lavished on them. That attention could prove an effective launch pad – but it could mean a very early collapse for any new venture.