So it's back to 1604 - the origin of the convention that the House of Commons cannot debate the same issue twice in the same session.

Speaker John Bercow said the government motion seeking parliamentary approval of the Brexit deal was the same one MPs voted on 48 hours previously.

On Saturday MPs backed the so-called Letwin amendment, requiring the government to get all of the necessary Brexit legislation passed first, and to seek an extension to the Brexit deadline from the EU if needed.

That longer path to approval opens the prospect of MPs trying to change the nature of the government's Brexit plans by amending the legislation to possibly include remaining in a customs union or holding another referendum.

The government will publish the Withdrawal Agreement Bill tonight, and seek to get it passed by the Commons and the Lords by early next week - a very challenging timetable. MPs will vote on whether to accept that timetable tomorrow.

It's that vote - on what's known as a programme motion - that could tell us a lot about how long it will take for the Brexit legislation to clear parliament.

The government hopes it can get the bill through all stages in the Commons by Friday evening, then make the House of Lords sit through the weekend, before finishing the process on Monday or Tuesday - or maybe even Wednesday - so that it can stick to the Brexit deadline of 11pm on Thursday week.

There is likely to be pushback from members, many of whom think it is a bad idea to rush legislation of this importance through parliament. Others will want to try and introduce amendments - remaining in the EU Customs Union, or a customs union with the EU are possibilities.

Making approval of the deal subject to a confirmatory referendum is another idea being promoted by the Labour Party.

And the Scottish National Party once again had an amendment ready for today's motion seeking a three-month extension to the Brexit deadline in order to hold a general election.

All of which leaves the EU with a dilemma: do the other states move quickly to grant an extension to give the parliament time to complete its legislative work over say a month or two?

Should they have a flexible arrangement allowing for a rolling series of Brexit start dates - whenever the ratification has been done - Brexit takes effect the following Wednesday (say)?

And what about the European Parliament? It too must ratify the Withdrawal Agreement, and seems minded to do so only after the UK parliament has done its work. Scheduling that adds an additional (though easier to manage) layer of complexity to an already complex situation.