Theresa May has asked EU leaders for a further delay to Brexit to 30 June.
As Philip Hammond said to me, the EU is very likely to insist on a much longer extension (if any) - unless the PM and Jeremy Corbyn can demonstrate by Wednesday's EU council meeting that they have agreed a way forward not only to approve the Withdrawal Agreement by then but also ensure the passage of the crucial accompanying legislation, the Withdrawal Agreement and Implementation Bill. Proving to the EU that the UK would not need yet another extension to avoid a no-deal Brexit currently looks a huge stretch.
And the point is that EU leaders do not want the UK to be constantly bothering them with further requests for Brexit delays. So the PM could be forced to accept either a Brexit delay of a year or so, or indeed (still not impossible) a no-deal Brexit on 12 April.
PS The PM has confirmed the UK will now start proper and expensive preparations for participating in elections to the EU parliament, even though the UK voted to leave the EU, and even though May is hoping the EU will allow her to cancel the actual casting of votes by UK citizens the day before the poll is due to happen on 23 May, if parliament actually agrees and implements her Brexit deal by 22 May. Many would say this makes a mockery of an important EU democratic process.
PPS By requesting a delay to "just" 30 June, Theresa May is trolling those who want a confirmatory referendum, or people's vote, because that delay is nowhere near long enough to accommodate a referendum. She is also trying to embarrass Jeremy Corbyn into agreeing a Brexit compromise before Wednesday, because if he doesn't she will be able to accuse him of blocking a short Brexit delay to "just" 30 June and wanting to trap the UK in the EU for much longer. This is raw brutal politics.
UPDATE 10.40 By the way, sources close to the PM were saying yesterday that the Tusk letter didn't need to be sent till next week - which is why many will say that sending it today, before Corbyn talks have reached any kind of conclusion, is aimed more at pressurising Labour’s leader into an entente (and at placating Brexiters in May's cabinet) than at EU leaders (who already rejected 30 June as a leaving date just a few weeks ago).