Theresa May (pictured in Downing Street) is struggling to thrash out a deal with the EU ahead of Brexit day in March

Next round of negotiations, September 21 to mid-October

After the Salzburg summit meltdown, the coming month of detailed talks will be among the most crucial so far.

The UK and EU negotiators are scrambling to break the deadlock so they can frame a 'political declaration' on the future relationship and finalise the withdrawal treaty.

How far they get in drafting the documents - and how much is left to EU leaders themselves - will determine when, if at all, an agreement can be struck.

The political declaration will explain in non-legal language what the two sides plans to agree in the final treaty.

A political declaration was used in December 2017 to outline the proposed transition deal and the £39billion divorce bill agreed by the UK. This is what is currently being turned into legal language for the withdrawal treaty.

EU Negotiator Michel Barnier (right in Brussels last week) maybe given new guidelines this week within which to strike a deal. EU Council President Donald Tusk (left) has said the meeting must reach a 'common view' on the shape of the future UK-EU relationship

EU Summit, Brussels, October 18-19

October's EU summit has long been pencilled in as the opportunity for EU leaders to agree the withdrawal treaty on the terms of exit and a political declaration on the future relationship between the UK and EU.

If a deal can be struck in October, it leaves plenty of time for it to be agreed in the UK and ratified in the EU, paving the way for an orderly Brexit in March.

A deal is not expected to be finalised at this summit but both sides will hope for significant progress - even if the summit is used to set out the dividing lines one last time.

Emergency EU Summit, Brussels, November 18-19

An emergency summit in November is now widely expected. If it happens, there will be acute political pressure to finalise both the withdrawal treaty and political declaration - if nothing else to allow the EU to return to other business.

Expect a high stakes meeting and a late night finish. Failure will see both sides walking up to the brink of a chaotic exit and peering over the edge.

The response of the European Council (including German Chancellor Angela Merkel) will be crucial in the next stages of the EU talks

EU Summit, Brussels, December 13-14

Given the need to ratify the deal, the December summit is the last chance to strike a deal. Brexit is not supposed to be on the agenda: if the talks reach this summit there has been a major breakdown.

The EU does infamously find a way to agreement at the 11th hour and if Brexit talks are still live in December, many will hope for a fudge that can get both sides over the line.

Last year, talks on the outline divorce deal were pushed to December and a deal was - just - reached.

The so-called 'meaningful vote' in the UK Parliament, January 2019

Assuming there is a withdrawal treaty and political declaration, the next stage is for the action is in the UK Parliament.

Mrs May promised Tory Remain rebels a 'meaningful' vote on the final deal in both the Commons and Lords.

This is expected to be a simple yes or no vote on what she has negotiated - so in theory a detailed withdrawal treaty, spelling out the divorce bill and other issues such as citizens' rights, and the political declaration on the future relationship.

Linking the two will be a high stakes moment. Brexiteers do not want to sign off the divorce bill without a trade deal and Remainers are reluctant to vote for a blind Brexit.

But the Prime Minister has made clear it is deal or no deal: accept what she has negotiated or leave Britain crashing out on March 29, 2019 with no agreement in place.

If the meaningful vote is passed, there will be a series of further votes as the withdrawal treaty is written into British law.

The Prime Minister (pictured at the EU Council in June) has made clear it is deal or no deal: accept what she has negotiated or leave Britain crashing out on March 29, 2019 with no agreement in place

Ratification in the EU, February 2019

After the meaningful vote in the UK, the EU will have to ratify the agreement. This is a two stage process.

National parliaments in all 27 countries have to vote on the deal. It does not need to pass everywhere but must be carried in at least 20 of the 27 countries, with Yes votes covering at least 65 per cent of the EU population.

The European Parliament must also vote in favour of the deal. It has a representative in the talks, Guy Verhofstadt, who has repeatedly warned the deal must serve the EU's interests.

In practice, once the leaders of the 27 member states have agreed a deal, ratification on the EU side should be assured.

Exit day, March 29, 2019

At 11pm on March 29, 2019, Britain will cease to be a member of the European Union, two years after triggering Article 50 and almost three years after the referendum.

Exit happens at 11pm because it must happen on EU time.

If the transition deal is in place, little will change immediately - people will travel in the same way as today and goods will cross the border normally.

But Britain's MEPs will no longer sit in the European Parliament and British ministers will no longer take part in EU meetings.

Negotiations will continue to turn the political agreement on the future partnership into legal text that will eventually become a second treaty. Both sides will build new customs and immigration controls in line with what this says.

If there is no deal, there is little clarity on what will happen. Britain has outlined contingencies for a catastrophic breakdown in transport and goods networks; in practice short term, small side deals will be likely be rapidly negotiated to avert the worst consequences.