Now that the UK Parliament has again rejected the Withdrawal Agreement and reiterated its desire to not leave without a deal, speculation is rife as to whether the UK will apply for an extension to Article 50, on what grounds, and for how long. Such an extension must be approved by the European Union and, if I'm not mistaken, by all member states. Undoubtedly, that approval process itself takes time. Is there any specific deadline on the latest possible date on which the UK can apply for an extension to Article 50?
All the articles that I can find discussing the matter state that an extension to Article 50 must be unanimously approved by the 27 member countries, which in practice appears to mean the EU Council or heads of state of each member country.
There is an EU leaders' summit scheduled for 21 to 22 March, during which a formal request for an extension could be made and approved.
This is based on Section 3 of Article 50.
- The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
So the deadline appears to be the 20th a March for a decision in the UK Parliament so it can be taken to the EU Leaders' summit on the 21st. There is no requirement for the EU Parliament (MEPs) or EU Commission (President and Commissioners) to approve or mechanism for them to reject the request for an extension.