One of the great lessons of the 20th century is that history has no direction: as Isaiah Berlin and Karl Popper argued, and as the transformative upheavals of 1989 showed to thrilling effect, there is no secular version of providence, no ideological script to follow. So it has been alarming, in the past few years, to watch the two main parties surrendering to different versions of the teleological delusion.

The Conservative party has embraced Brexit as a mythic nativist destiny towards which we must all march loyally. Labour, meanwhile, is in thrall to the old left determinism, in which all the core debates have long since been settled, devotion to the leadership must be absolute, and all that remains is for those who are foolish enough to think otherwise to be stripped of their false consciousness. For those of us who believe in pluralist politics, it has been a depressing spectacle, a battle between desperate certainties that slide pointlessly over the gritty, unpredictable reality of 21st-century life. Which is the principal reason why the foundation of the 11-strong Independent Group of formerly Labour and Tory MPs has been so refreshing.

Rudd, Gauke and Clark have issued a flagrant challenge to the last sacred principle of Mayism

I have been sceptical in the past about the notion of a new centre party – but am pleased to have been (thus far) confounded. As Heidi Allen and Luciana Berger showed on the BBC’s Andrew Marr Show, the group has no intention of being pressed into announcing policies prematurely, rushing to form a party hierarchy, or of seeking to disguise their differences. Instead, they are turning these disagreements into a strength and striving – in Chuka Umunna’s words – to be “culturally different”. They will prosper to the extent that they make good this promise. They must put strategy before tactics (incredibly hard). They cannot afford to look like the liberal elite demanding its job back. They must be rigorous in addressing new challenges rather than re-litigating old battles. They must continue to act with dignity in the face of seething social media fury – especially strong from some Corbynites, whose treatment of the escapees has been reminiscent of Scientology’s hounding of “suppressive persons”.

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But what the independents have already done is important: more important, perhaps, than the formation of the Social Democratic party in 1981. The “gang of four” was a breakaway faction of the Labour party. The Independent Group has genuinely bipartisan roots. And – unlike the SDP – it is starting its life in the crucible of a full-blown constitutional crisis.

Whether it succeeds or fails, it has already acted as a much-needed solvent of the certainties that have paralysed Westminster during the Brexit process. It has reintroduced the indeterminacy principle to mainstream politics and, most specifically, shown those who fetishise the 2016 referendum result as if it were the burning bush of our era – a quasi-divine mandate – that leaving the EU is still, as a matter of fact, entirely voluntary. We can still step away from the precipice, if we choose, as a nation, to do so.

Even as the 11 coalesced, three cabinet ministers – Amber Rudd, David Gauke and Greg Clark – published a truly remarkable article in the Daily Mail signalling their support for an extension of article 50 to prevent a no-deal outcome “if there is no breakthrough in the coming week”. It is hard to exaggerate the significance of this intervention. Theresa May’s defining mission – her reason for remaining in the job – is to take Britain out of the EU on 29 March. With a degree of repetition remarkable even by her standards, she has said that no-deal must stay on the table as a bargaining chip.

Rudd, Gauke and Clark have issued a flagrant challenge to this, the last sacred principle of Mayism. And they have done so, thus far, with impunity. They know full well that a formal delay would smash to pieces the framework within which the Commons has operated since backing the government’s article 50 bill in February 2017.

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It would, for a start, dramatically oxygenate the argument in favour of a further referendum. It is already gaining fresh momentum, as Labour edges towards something approaching endorsement. In his fractious Sky News interview last week, Jeremy Corbyn made clear that he still loathes the idea, and would only countenance a public vote on a Labour deal: a precondition of which, presumably, would be the election of a Labour government. Deputy leader Tom Watson came much closer to the centre of gravity of opinion in his party on Sunday, when he said that Labour should back a fresh referendum if May rejects the party’s five-point Brexit plan (which she already has). This week, even though the meaningful vote has been postponed again, MPs will be given the chance to vote on Yvette Cooper’s amendment that would seize control of the parliamentary agenda and require the prime minister to seek such an extension (unless a deal is reached by 13 March). In January, Cooper’s binding proposal was defeated by a margin of 23 votes – while Caroline Spelman’s nonbinding motion against no-deal secured a majority of eight. In other words: we’d like to do the right thing, but we’re not allowed to. Sorry.

On Wednesday, there will be only 30 days left until the official Brexit date. If that doesn’t focus the mind, I don’t know what will. Those wavering MPs who still feel constrained by narrow ideological loyalties, the haranguing of the whips, the dead slogans of a three-year-old campaign, should look at the 11 MPs who decided to cast aside those chains. They should ask themselves whether, for once, the claims of the public interest, of common sense and of future generations might just trump all else. They should ask: if not now, when?

• Matthew d’Ancona is a Guardian columnist