I have little doubt the EU would agree an A.50 extension by the required unanimous consensus if requested by the UK, and if presented with a clear rationale for doing so - e.g. to enable the UK to hold a general election or second referendum. The extension would therefore likely be in the 1-3 month range to facilitate the above, although there is no reason the Council could not grant a second extension if deemed necessary.

The unanimity requirement becomes problematic if the purpose is merely to enable the UK to re-open and extend negotiations on the current deal. A new government might be extended that privilege if its stated re-negotiation objectives were not incompatible with EU interests - e.g. full membership of the Single Market or Customs Union - although the hostility of some to Corbyn would not be helpful.

If the new government were led by someone like Boris Johnson whose main objective might be to grandstand and shift the blame for a breakdown to the UK the probability of a further A.50 extension approaches zero. It would be ironic if it were the EU27 which finally lost patience with the UK and effectively booted it out by refusing to extend A.50.

Of course until the notice period or any agreed extension thereof expires, the UK retains the agency to revoke the A.50 notification entirely, even if its intention is merely to play for time and re-invoke it some time later. The ECJ ruling (para. 76) that any such revocation must be:

1. In writing to the Council
   
2. In accordance with that members states own constitutional procedures, and
   
3. unequivocal and unconditional

Does not include the Advocate General's condition, included in his Opinion and guidance to the Court (para. 170) that any such revocation must be done in good faith and does not involve an abusive practice. Therefore, conceivably the UK could invoke and revoke A.50 ad nauseam just to annoy the rest of the EU. Of course no one would pay any notice to them if they decided to adopt such tactics.

Index of Frank's Diaries