It's less than 300 words, but this document will change Europe's future

Britain’s vote to leave the EU has already been hailed as one of the most momentous events in Europe since the fall of the Berlin Wall in 1989. Exiting the EU is the central task that Theresa May, the new prime minister, has set herself — even though she herself voted to remain in the bloc.

But how and when the UK will break up with Brussels is far from clear. Much depends on an innovation in the EU treaty — Article 50 sets out how a member state can break up with the bloc.

The UK’s future may rest on this text of fewer than 300 words, and how they are interpreted.

Why is Article 50 important?
In theory there are other means to leave the EU, but both the UK and the EU have agreed this would be the process for Brexit. To start the Article 50 process, the UK needs to make a formal decision to leave the EU and notify the EU Council of member states of this decision.

Why was the referendum not sufficient?
The referendum was not legally binding. Parliament could have chosen to make it legally binding but it did not. It was, in its legal effect, a consultation exercise.

Why has the Article 50 notification not been sent?
During the referendum campaign David Cameron, then prime minister, said that in the event of a Leave vote, people would expect the notification to be made straight away. When he announced his resignation, however, he said this would be a matter for his successor.

What legally needs to happen before the Article 50 notification is sent?
The legal position is not clear. Some constitutional experts say triggering Article 50 needs a statute, while others say it can be done by the prime minister exercising the royal prerogative. It seems that the government may fudge this, and have a parliamentary vote on repealing the European Communities Act before any things are done by prerogative.

Some lawyers have filed a legal action to force the government to have a parliamentary vote but they are unlikely to succeed, as the courts may see this as a political and not a legal matter.

What else needs to be done before the Article 50 notification is sent?
Pretty much everything. There is no clear plan. David Davis, a veteran Eurosceptic, has been appointed to head a new Brexit department, as secretary of state for Exiting the EU. But he faces an immense and complex task.

Can the UK negotiate with the EU before sending the Article 50 notification?
The UK would like to do this, but the other member states are not obliged to negotiate until the Article 50 notification has been sent. They are being firm on this, and this may convert into a stand-off. In the meantime, the UK remains a full member of the EU.

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What happens once the Article 50 notification is made?
Once triggered, there will be a maximum two-year deadline for exit. At the end of two years, even if no agreement has been reached, the UK will cease to be an EU member state. The deadline can only be extended by unanimous consent. In theory, Britain could leave in less than two years if there is agreement.

Can the UK withdraw from the exit process once Article 50 notification is made?
Nobody knows, and Article 50 is silent. If there was unanimity, then there would not be a problem. But it would be a risky tactic, and may not work.

What would an exit agreement look like?
The exit agreement could be either narrow, dealing with just the terms of departure, or it could conceivably also address the UK’s future relationship with the EU. It could be followed by a trade deal or series of trade deals.

Is Article 50 notification inevitable?
Mrs May has suggested that she will trigger the exit procedure around the end of the year. She has also said Britain will not start the process until it has thrashed out UK-wide objectives for the negotiations. Other defeated contenders for the leadership had called for earlier notification. But Mrs May dismisses the idea that delay increases the likelihood of Article 50 never being used. “Brexit means Brexit and we are going to make a success of it,” she said last week.