Parliament is expected to sit on Saturday, October 19 in what could be one of the most important Commons’ sessions of the entire Brexit process. It will consider the Brexit deal that Boris Johnson has secured in Brussels.
Parliament has only sat on a Saturday on three occasions since the outbreak of the Second World War, and even before then it was a rare occurrence. The last time the House of Commons convened on a Saturday was after Argentina invaded the Falklands in 1982.
Why will they sit?
On October 17, Mr Johnson secured a series of changes to the Brexit Withdrawal Agreement and Political Declaration.
The changes to the former mean that the backstop is replaced by an effectively permanent protocol which applies to Northern Ireland only and leaves the whole of the UK to negotiate free trade deals around the world. The changes to the latter loosen the provisions which would have stopped Britain from deregulating.
Parliament must now consider the deal and vote on whether to approve it. If it rejects the deal then the so-called Benn Act requires the Prime Minister to request an extension to the Brexit process.
With the DUP refusing to support the deal, the vote could be incredibly tight and will depend on whether Mr Johnson can retain the support of his own hardliners while also winning back former Tories and convincing two dozen or more Labour MPs to rebel against their leader.
What other options could MPs take?
MPs could reject the deal outright. If they do, the Government has confirmed that Mr Johnson will ask for an extension. However, he could try to undermine that request and MPs could be forced into a vote of no confidence to remove the PM.
If they do that they would need to try and form a so-called unity government to secure an extension and perhaps legislate for a referendum. Eventually, there would need to be a general election.
Another option could be for MPs to attach a confirmatory referendum to the deal, so that the country would vote again. There have been reports that Jeremy Corbyn now supports such an approach. However, it's unlikely that a parliamentary majority for a referendum could survive the many, many votes to pass a referendum law.
MPs could also try and amend the deal in other ways, for example by forcing the Government to pursue a softer Brexit in the future relationship negotiations.
Whatever the outcome, Saturday 19 will be an historic day.