Today, the United Kingdom submitted its formal notice to the European Union in order to trigger Article 50 of the Treaty on European Union (the Article 50 Notice). This is the formal mechanism which begins the two-year process of negotiating the UK’s exit from the EU.
The UK will leave the EU by 29th March 2019 at the latest (unless all EU Member States agree unanimously to extend the negotiating period – which currently seems unlikely).
During the negotiation period, EU laws will still apply to the UK. The UK will not participate in discussions or decisions within EU institutions relating to its own withdrawal, but will continue to participate in other EU business as normal.
The negotiations will cover matters including the trading of goods and services, immigration, financial passporting rights and a new EU-UK regulatory framework.
Matters decided in negotiations will also need to be approved by a majority of EU leaders, MEPs, and potentially also national parliaments and some regional parliaments.
In short, there is a large amount to be negotiated and approved by a significant number of organisations during a two-year period. It is possible that there will need to be transitional arrangements for some existing arrangements while the UK and the EU continue to negotiate after the end of the two-year period.