And as I say; nor *would* they even if they could. All 27 governments must agree unanimously to the terms of the extension and countries like Hungary, Italy and Poland, who are currently in dispute with the EU, would never set a legal precedent that could later be used against them.
Let's be honest; none of us know what's going to happen later today in brexit... let alone in two weeks. But based on what I've read, the EU is likely to agree to an extension under two circumstances:
1) If it has a firm -- and likely quite lengthy -- minimum time limit. Some are speaking of two years. Others want it to be at the end of the next EU parliamentary term.
2) If the UK proposes a specific solution (i.e. if THEY suggest a second referendum, or a general election). Then the EU might grant a shorter extension to implement that.
The problem with (1) is that Theresa May doesn't want anything to do with it. Staying that long means running candidates in the EU elections without having Brexit resolved. A lot of people suspect that would be the final nail in the tory coffin, and having threatened it for 3 years, the party would finally split down the middle.
And (2) rests on the UK realising that it's up to them to resolve this now. They are getting no more from the EU than the Withdrawal Agreement and I'm still not sure this has sunk in with the tories. In order for this to work, they need to offer concrete concessions and a plan forward.
But instead they're demanding concessions from the other side and assuming that someone - anyone - else will develop and implement a plan on their behalf.
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EDIT / ADDENDUM: As an aside, I suspect it will be Option (1) by default... it's not like Theresa May has got her desired outcome too often in the last few weeks, so her opposition to it isn't sufficient to prevent it IMO.
If I had to guess; I think we're at the point where May will be offered a two-year, take it or leave it, extension by the EU.
She will hold another Commons vote -- Her original deal Vs a 2 year extension. This will scare a LOT of the rebels and the ERG onside -- they'd rather get out now and hope to torpedo the backstop later, than risk staying in for another 2 years and losing brexit altogether.
But I think she's still lose the vote, because the DUP won't fall in line and not ALL the tory rebels will come home.
The UK will enter a 2 year period of "associate membership" -- i.e. they will have full responsibilities but less input into decision-making (I suspect they will lose their veto on legislation for example; on the assumption that they will not be bound by it once the extension is complete).
In the meantime a general election will be held and at some point over the next couple of years, brexit will be cancelled entirely. The UK will gain full membership status; will likely retain opt-outs on the single currency and Schengen, but will lose the financial rebate and other special deals. It will also have lost a HUGE amount of internal influence within the EU that could take a decade or more to regain.
*puts down crystal ball*