In a crisis, imagination is as important as commitment – and Gina Miller has both. As 29 March hoves ominously into view, the investment manager, who successfully challenged the government’s authority to invoke article 50 without parliamentary approval, is making another significant intervention in the Brexit process – more subtle this time, but no less worthy of political and legal attention.

Having used the courts in 2017 to give parliament a say in the triggering of article 50, Miller is now, I gather, seeking to reframe the way in which Westminster and Brussels contemplate the possibility of its extension. Armed with a legal opinion written by Kieron Beal QC and three other senior lawyers, the co-founder of the pro-remain campaign Lead Not Leave will argue that the EU council of ministers could itself, unilaterally, extend the article 50 deadline.

Brexit: Labour will whip MPs to back second referendum, says McDonnell Read more

Why should it even contemplate doing so? First, because – as Miller’s legal paper points out – “the wording of article 50(3) presupposes that the European council take the decisive lead with the consent of the withdrawing member state”. Second, because the EU has a legal duty to all its member states to ensure that any such withdrawal is not damaging to what article 13(1) of the treaty on European Union calls the “consistency, effectiveness and continuity of its policies and actions”, or to the principle spelled out in article 13(2): “Pursuant to the principle of sincere cooperation the EU and the member states shall, in full mutual respect, assist each other in carrying out the tasks which flow from the treaties.”

Miller’s point, of course, is highly political as well as specifically jurisprudential. By circulating this opinion at the European parliament and in Brussels, she hopes to remind the EU that the legal, practical and moral obligation to prevent a catastrophic no-deal outcome is not confined to Westminster. Her message is addressed to figures such as Donald Tusk, the president of the council, and Jean-Claude Juncker, his counterpart at the European commission, but also to the EU body politic as a whole.

Does she really expect the council to trigger an extension unilaterally? Maybe not. But she is reminding the 27 other member states that they cannot, as a matter of law as well as of supranational ethics, play Pilate and wash their hands of this mess. We are, to coin a phrase, all in this together.

Self-evidently, this is an issue of the highest importance in the final days before the UK’s official date of departure from the EU. Last week, with a reluctance matched only by Jeremy Corbyn’s allergic embrace of a people’s vote, Theresa May conceded that, were she unable to secure the support of MPs for her amended deal, she would give them the chance to rule out a no-deal exit on 29 March and then to back a “short, time-limited extension” to article 50.

Facebook Twitter Pinterest ‘If an extension is indeed demanded, the EU has to be more than May’s dutiful enabler.’ Photograph: POOL/Reuters

As much as this concession clearly tasted like ash in the prime minister’s mouth, it was preferable to the resignation of as many as 25 pro-EU ministers – a clear and present danger, had she not relaxed her previously unshakeable position on the Brexit timeline. Predictably enough, the prospect of an extension has spooked hardline Tory Brexiteers and the Democratic Unionist party (DUP), who have depended all along upon the inviolability of Britain’s departure date. It is at least possible now that the European Research Group and the DUP will throw in the towel and back May’s amended deal.

But it is also feasible that – looking over the cliff edge – parliament will decide only to do so on the basis of the proposal put forward by the Labour MPs Peter Kyle and Phil Wilson: namely that the Commons backs the agreement, but then puts it to a public vote. It is entirely true that the parliamentary arithmetic does not yet favour a fresh referendum. But parliamentary arithmetic can change dramatically as circumstances blur and morph.

Europe can only give us more time if we have a clear Brexit plan | Tony Blair Read more

On 15 January, May’s deal was defeated by a majority of 230. Less than a month later, No 10 believes victory is entirely possible. Who is to say what the parliamentary configuration will look like even a week from now? The odds have always been against a people’s vote as merely one option among many on a tick-box menu of constitutional possibilities. It is an organic idea, rather than a static mechanism, and one that will only gain traction as the last resort of the truly patriotic – the choice of political maturity over populist madness.

Which is why Miller’s intervention is so important. If an extension is indeed demanded, the EU has to be more than May’s dutiful enabler, agreeing by rubber-stamp to extend article 50 for a period so short as to be all but meaningless.

For there is absolutely no point in spending a few more frantic weeks in limbo. Any prolongation that does not allow time for serious debate from first principles or is not long enough for a public vote – nine months at a minimum – will be no more than a shabby exercise in political theatre.

There is no intrinsic reason to assume that the EU or European parliament will heed Miller, or that the exhausted Westminster class will seize this opportunity. Then again, she has a record of defying the odds. At a moment of the most depressing political paralysis, her proposal holds the door open to fresh possibilities. Who, then, has the courage to walk through?

• Matthew d’Ancona is a Guardian columnist