The statement of the Conference of Presidents of the European Parliament has been an interesting development in the Brexit saga this week. The European Parliament is trying to impose a deadline at the end of Sunday 20 December for a political agreement between the UK and the EU, although they give a little more wriggle room with regard to when an actual text would need to be available (Manfred Weber says Monday for that).

The European Parliament’s rationale is obvious enough – they want to scrutinise the Deal before it enters into force, and although the timetable is ridiculously short still can do this before 1 January. An extra European Parliament plenary 28-29 December could be organised for this purpose. The statement this week is the EP saying in public what it has been saying to Barnier and his team for months – enough is enough, we cannot do proper scrutiny if this drags on further.

So what will happen?

The European Parliament could be successful – the deadline might actually work (Barnier, it seems, got a couple of days more from the EP than it had wanted to grant) and by the end of Sunday a Deal is on the table. If so ratification can proceed.

But what if – like so many Brexit deadlines – Sunday night comes and goes without an Agreement?

Here there are two options, although one has drawn a lot more of the attention than the other.

By far the best known route is Provisional Application – basically that the Member States of the EU and the UK would agree the Deal, and this would then be OKed by the European Parliament only after 1st January. How this can work, legally, is explained by Georgina Wright here. Others such as Sam Lowe and Tony Connelly think this is likely the route the European Commission will propose. There is nothing the European Parliment could actually do about it if the Commission proposed Provisional Application – the Council can choose to proceed and the European Parliament cannot stop it.

But there are downsides and dangers to Provisional Application. If the European Parliament is to have a say after the fact, why should the same not happen for national and regional parliaments (Elio Di Rupo has said as much). The delicate consensus that the Brexit Deal is an EU-only Agreement (not a Mixed Agreement needing national and in the Belgian case regional ratification) could shatter quickly. And more importantly overall EU unity on Brexit matters could break – with the European Parliament being directly contradicted by the other EU institutions. Plus letting the clock run down even further would be a vindication of the UK strategy to do all of this at the very last minute, something that does not sit easily with an EU that is meant to have better procedures.

Above all the political argument that the European Parliament can make against Provisional Application is a strong one – it is impossible to proper parliamentary scrutiny after a Deal has entered into force.

The alternative option is a mini Treaty, to carve out more time for negotiations to conclude. This route has been largely ignored until now, but could well rear its head on Monday.

The line would be like this: we, the EU, have shown every flexibility available. We have worked as hard as we can, and a Deal is still in sight. But were this to drag on any more we simply do not have time to do the necessary parliamentary scrutiny on our side. And, dear Brits, we know that you too cherish the role of your Parliament in processes as complicated as this. So we offer you an extra month to conclude everything – so both sides can actually do this process with the care it deserves.

To do this the UK and the EU would have to agree a mini Treaty that de facto extended the Transition Period by a month. Agreeing this would be simple on the EU side – it would need EP approval too, and perhaps even Provisional Application – but that would not prove a problem*. EU unity would be preserved. The European Parliament would be relieved. Indeed even Member States of the EU would breathe a sigh of relief, as it would give their administrations extra time to check for any gremlins buried in the text.

The big question of course would be: what would the UK do?

Were Johnson to agree to an extra month, his backbenchers would scream – that there should be no extensions to the Transition Period is about the only thing that holds the Tory Party together on Brexit. But if Johnson declined the offer that sends the UK over the cliff to No Deal and the problem is Johnson’s and Johnson’s alone. “We stood ready to help,” the EU can say, “but the offer of a little more time was declined by the UK.”

So then European Parliament, over to you to make this demand clearly and simply: if there is no agreement by the end of Sunday, from Monday morning a mini Treaty to extend the deadline is obviously the better route.

* – this sentence has been adapted to make it clearer that the EP would have to OK this route, in light of this tweet from Mark Johnson.