At the moment, it seems almost certain that the UK will give an “article 50” notice to leave the European Union – although the timing of the notice is uncertain.
It is at least possible that attempts will be made to block the giving of this notice. If they fail, attempts may also be made to hold (a) a second referendum, in the hope that the electorate will make a different choice on the second occasion; or (b) a general election, with at least one of the parties pledging to keep the UK in the EU, if it’s elected. The timing of each of these things is also uncertain.
If the article 50 notice has been given, and the circumstances warrant it, can the giving of that notice be undone?
Article 50 only seems to have a forward gear: the notice is given, and up to 2 years of negotiations follow. If an agreement is reached, the UK withdraws on the negotiated terms. If it isn’t, the UK’s membership lapses automatically – unless all 28 Member States of the EU agree that the time for negotiation should be extended.
There’s nothing on the face of article 50, which suggests that a notice, once given, can be cancelled or withdrawn. But the 28 Member States could agree that the notice has been, or will be, cancelled or withdrawn nonetheless. It might also be possible to achieve the same result with the consent of the European Parliament, and a qualified majority of the Council. The giving of the article 50 notice could therefore be undone – if the political will can be found.