The supreme court decision was predictable, but momentous nonetheless – a reaffirmation of the result of the Civil War, namely that parliamentary sovereignty trumps executive power, whether the executive is the king or Theresa May and her cabinet. Article 50 cannot be accessed other than by a statute passed by parliament, which repeals the 1972 European Communities Act. Parliament took us into Europe, and only parliament can take us out.

The bad news for May is that this means her “great repeal bill” must be a fully-fledged piece of legislation: its length may be short, but its time of passage will not, if MPs do their duty and discuss it, both in the House of Commons and in committee, and peers debate it in the Lords and make use of their power to remit and delay.

Although both major parties seem wedded to the claim that “the British people have decided to leave”, the British people have done no such thing. At the referendum last June, 37% of those eligible to vote supported Brexit, 35% wanted to remain and 28% did not vote at all – many, in my view, misled by opinion polls indicating a pro-Europe result. Since 63% of the British public did not vote to leave, there would seem plenty for parliament to debate: whether a non-binding referendum should be allowed to produce a further fall in the currency, for example, or diminish human rights.

Brexit: rebel Tories demand more say on Brexit as May loses supreme court fight Read more

Whether MPs and peers will do so is an open question which will test their own integrity. Parliamentarians have a duty, by constitutional convention, to speak and vote according to their conscience and what they honestly consider to be in the best interests of the United Kingdom, irrespective of the opinions of their constituents. Although this duty was first laid down by that redoubtable conservative Edmund Burke, Europhile Tories other than Ken Clarke seem reluctant to do it. As for Labour, who knows? Its policy in the lead-up to a referendum that the supreme court now confirms had no legal effect, was to remain. That is also the policy of the Liberal Democrats and the Scottish National Party. Might a coalition – now, or in some future parliament – reverse Brexit?

The supreme court decision is clear: parliamentary sovereignty means that we cannot leave Europe without parliamentary passage of the great repeal bill. What is less clear – and what the judges have deliberately left opaque – is whether, once article 50 is triggered, it can be reversed before the UK has to depart Europe within two years (unless all 27 members allow us more time).

The supreme court assumed – for no better reason than counsel on both sides agreed – that triggering article 50 was irrevocable. But the judges in the majority went out of their way to state that they did not necessarily agree with this assumption, which had not been argued, and one dissenting judge described it as “possibly controversial”. So here is the great remaining, unresolved question: does article 50 start an inexorable Brexit from which the UK cannot withdraw, or might another parliament repeal May’s great repeal act in the future, before we have actually left?

Might a coalition – now, or in some future parliament – reverse Brexit?

The answer may lie in the simple principle that in this representative democracy parliament may do virtually anything. This year, May might induce it to repeal the 1972 European Communities Act, but next year it might decide to repeal her great repeal act (2017), and to remain in Europe. Although this was not the view of the parties in the supreme court, it follows both from the judgment and from the language of article 50 itself, which tells a departing state that it “may decide in accordance with its own constitutional requirements”. So unless de-Brexit is blocked by European states fed up with the UK by this stage, it would be possible for a future parliament to decide to withdraw from the Brexiting process.

The real message from the supreme court is that it is early days yet. It gave the government some relief by ruling that devolved assemblies have no right to throw spanners in the Brexit works. But its core decision is that the determination must be made by both Houses of Parliament. It is absurd for tabloids to protest about “enemies of the people” and the power of “unelected judges” – the supreme court judges were not exercising power themselves, but rather deciding which institution of government should exercise it.

Their verdict in favour of parliament now casts responsibility upon elected MPs and appointed peers. What “the people” must now expect from these their representatives is careful and conscientious debate about whether May’s plan (which should be fully revealed) will make Britain great again, or turn it into a bargain-basement offshore tax haven with sunken sterling.