What is meant by the UK triggering Article 50?

This involves the UK serving notice on the European Union ("EU") of the UK’s intention to leave the EU. The notice is served under Article 50 of the Treaty on European Union.

What are the requirements for triggering Article 50?

Surprisingly few – but it has proven difficult with court cases and controversy surrounding it – Article 50(1) simply provides that the Member State must act in accordance with its own constitutional requirements and then the article sets out some basic steps.

Who receives the Notice? What is in the Notice?

It is received by the President of the European Council (Donald Tusk). It is presented to the President by the UK's Permanent Representative to the EU. It is in the form of a letter from the UK announcing its intention to leave.

Is the Article 50 notice reversible?

Article 50 does not specify either way whether it is reversible or not but it is generally (but not universally) believed to be reversible so it seems likely that the UK could reverse the notice at some stage in the future.

Does it mean that the UK will leave two years after the serving of this notice?

No. Article 50(3) provides that the EU 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 [Article 50, paragraph 2], unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.”

So, it is not inevitable that the UK would leave two years from the serving of the notice. There are actually three possible dates: (a) the date specified in the agreement; (b) a date agreed by the European Council and the UK (assuming no agreement and assuming the 28 reach agreement on a date); or (c) two years from the date of the serving of the notice in default of the other two scenarios. So, the two year date is the fall-back position and not the inevitable outcome.

If the UK leaves then could it simply re-join at another time?

No, Article 50(5) provides that the UK would have to re-apply and go through the normal route which takes a number of years.

What does all this mean for business?

At one level, nothing because the UK is still bound by the rules. In practice, it means that the “phoney war” is over and businesses should sit down, identify which EU law rights are they dependent on, consider which proposals they need to make to their own Government and the EU to ensure that any Brexit deal meets their needs.