People once dreamed of a Brexit that would give Britain more control and free us from paying anything to Brussels, while opening up the prospect of huge new trade deals and “the exact same benefits” we have today as EU members.

Now, in the cold light of a Brexit dawn, we have a withdrawal agreement that will see the European court handing down rulings binding on the UK for years – if not decades – to come, with us trapped in a backstop deal from which, as the attorney general has confirmed, there is no unilateral escape. Meanwhile we would face endless negotiations to create what would only ever be second-class access to Europe’s markets and, lest we forget, a £50bn divorce bill.

Little wonder that the government has had to look for other arguments to support the deal. What it has hit on is that an alternative to its Brexit is an even worse Brexit. It talks up the prospect of a “no-deal” option – of jammed ports, grounded aeroplanes and emptied supermarket shelves – with the same relish that bad parents use when trying to scare their children into bed with tales of monsters.

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But we now know that the idea that this choice – a bad deal or no deal – is as much a fantastical nightmare as the earlier promises about Brexit were a dream.

This week the advocate general of the EU’s court of justice published advice to the court about the revocability of the UK’s withdrawal from the EU under article 50 of the EU treaty. He has confirmed that we have an absolute right to change course and take back our withdrawal notification without paying any price – financial or political.

I admit this is something of a specialist subject for me: I was secretary general of the European convention that drafted the article. I have always believed that nothing in it restricted our rights as a full EU member to change our minds, stay in and keep all our current rights, privileges and opt-outs: Margaret Thatcher’s budget rebate, John Major’s exemption from joining the Euro, Theresa May’s opt-in to the European Arrest Warrant and Europol.

I was not, therefore, particularly surprised that the advocate general advised the court in the way he did. The full court could disagree, but such reversals are rare.

Even as the court was confirming that staying in the EU was an option, the idea that we might slide out without a deal was being cleared from the table. Dominic Grieve and Chris Bryant, in different parties but both experts on parliament and the constitution, came together to list six further ways in which parliament could put the brakes on any attempt to pull the UK out with no deal. The defeat of the government on the procedural amendment tabled by Grieve provides a guarantee that MPs will have a proper say over what happens next.

The long and the short of it is this: the idea that no deal is either a credible threat in frightening MPs, or that it is the default option if we reject the deal have both been killed off. There is no bar on parliament preventing no deal and no responsible government would ever want to force the country into it, when it knows it is so easily stopped.

The real debate now is between leaving under the humiliating terms of the proposed withdrawal agreement, with no certainty about the eventual permanent relationship, or staying with our current rights as full members, with a voice, a vote and veto.

So the choice is between a bad Brexit deal and sticking with the deal we have in the EU. And it’s a choice for the people. I don’t think it would be right for parliament to just vote to stop the Brexit process. The people started this with their vote and they must make the final decision.

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Almost certainly that will require some extension of the article 50 deadline beyond 29 March. The treaty is very clear about this – it can be done but requires unanimity among all EU states. If our purpose in asking for an extension was to allow time for a referendum, there is no doubt that all would agree. Brexit would be bad for everyone, though obviously worst for us.

And that leads me to one more, final, Brexiter fantasy, that we would ask for an extension to negotiate a “better” Brexit. For that there is no enthusiasm in any European capital. Dreams of a Norway-for-now-or-ever are just that – dreams.

The deal we have been offered is not what was promised and it’s not nearly as good as the deal we’ve got in the EU, but it’s the only Brexit offer on the table.

Today was the day the terms of the debate changed because, if MPs and ultimately the British people, think it’s a bad deal, we know we can reject it without fear.

• Lord Kerr drafted article 50 and is a former UK ambassador to the EU