The vote for Britain to leave the European Union inevitably leads to the question of how that will be achieved.
Politicians discussing the referendum result will cite Article 50 of the 2007 Lisbon Treaty, the mechanism by which a member state can leave the union.
David Cameron, in announcing his resignation as Prime Minister, said he would leave it to his successor to invoke the law, meaning it will not happen until after a new leader is in place in the autumn.
Labour leader Jeremy Corbyn said the process should begin immediately but others, including Leave campaigners Liam Fox and Andrea Leadsom, have said it is right to hold off.
When the UK does trigger Article 50, it must formally notify the EU of its intention and begin a period of negotiation over the UK’s future relationship with the union lasting up to two years.
The article states: “The Union shall negotiate and conclude an agreement with that state, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the union.
“It shall be concluded on behalf of the Union by the (European) Council, acting by a qualified majority, after obtaining the consent of the European Parliament.”
The two-year period starts when a member state informs the European Council of its intention to leave but can be extended by a unanimous vote of the Council members.
If a deal can be reached within two years, EU treaties will cease to apply from the date that agreement enters into force.
But if no deal on withdrawal is achieved – and any of the other 27 states block an extension of talks – membership ends automatically after the two-year period, leaving the departed state to operate under international rules set by bodies such as the World Trade Organisation (WTO).
Some Remain campaigners argued during the campaign that shortly after invoking Article 50, the UK would find itself considering Article 49 – which sets out the conditions for rejoining.