LONDON/BRUSSELS (Reuters) - With just six months to go until Britain is due to leave the European Union, negotiations between the sides to agree a divorce settlement and a blueprint of new relations after Brexit are in the final stretch.

FILE PHOTO: An official inspects a Union Jack flag next to the European Union flag, ahead of a meeting between Britain's Secretary of State for Exiting the European Union, Dominic Raab, and European Union's chief Brexit negotiator, Michel Barnier, at the EU Commission headquarters in Brussels, Belgium July 19, 2018. REUTERS/Francois Lenoir

If they fail to agree, Britain could face leaving without a deal, a national election or even another referendum.

Below are significant dates in the run-up to Britain’s scheduled departure from the EU in March:

IRISH PM IN BRUSSELS - Oct. 4

Ireland’s Prime Minister Leo Varadkar holds talks with EU officials on Thursday, as Britain and the bloc make a new push to overcome their differences on the post-Brexit Irish border.

BARNIER MEETS N. IRELAND POLITICIANS & EU 27 ENVOYS - Oct. 5

EU Brexit negotiator Michel Barnier meets Northern Irish politicians but not Democratic Unionist Party leader Arlene Foster who vehemently opposes having different regulations on her soil to the rest of the United Kingdom.

A meeting with Foster is expected next week.

Barnier will also brief Brussels ambassadors of the EU 27 states on progress.

“OUTLINE OF NEW PARTNERSHIP WITH UK” - Oct. 10

Barnier is due to present to the EU’s executive European Commission a first draft of the bloc’s proposal for close trade ties with Britain after Brexit.

EUROPEAN COUNCIL - Oct. 17-18

May meets fellow EU leaders and the European Commission to try to seal deals on the terms of Britain’s withdrawal and what kind of relationship it has in the future.

EU leaders of the 27 states remaining in the bloc will have a dinner on Wednesday and then hopefully be joined by May on Thursday to announce enough progress has been made on the Irish border issue to merit calling an extra EU summit in November to finalize the deal, including a blueprint of future trade ties.

SPECIAL BREXIT SUMMIT - weekend of Nov. 17-18

EU leaders are ready to hold a special summit on the weekend of Nov. 17-18 to seal a Brexit deal with Britain, if agreement had been reached.

Markets are expecting a deal in November, and analysts say sterling would likely fall if the talks slip further.

EU COUNCIL - Dec. 13-14

European Union leaders will gather for an EU Council meeting on Dec 13-14. If a deal is not struck in November, this summit could be one of the last chances for a deal if parliaments on both sides are to ratify an agreement by exit day in March.

UK PARLIAMENTARY VOTE ON BREXIT DEAL - Unscheduled

If May secures a deal, she has to get the British parliament to approve it. She would need about 320 votes in parliament to get approval.

Her Conservatives hold 316 seats in the 650-seat lower house, and she relies on a Northern Irish party to win parliamentary votes.

Labour has indicated it would vote against her deal so unless she can win over her own lawmakers, she could lose a vote in parliament.

Failure could trigger a move against her leadership of the Conservative Party, or the government’s collapse and an early election.

EUROPEAN PARLIAMENT RATIFICATION - Unscheduled

The European Parliament must also sign off on any agreement reached between May and the other 27 EU leaders. If the legislature starts ratification in November or even December, it should still be able to complete the elaborate process in time for Brexit day.

It could hold a final vote during a plenary session set for March 11-14. But legislators’ minds will also be on campaigning ahead of European Parliament elections in May - in which Britain would no longer take part.

EU officials have suggested a further delay may still be possible if negotiators are very close to sealing a deal. But it would just be a few extra weeks at best, as the current EU parliament holds its last plenary session on April 15-18, 2019. That is already beyond the current Brexit date.

NO DEAL STATEMENT

If there is no deal by Jan. 21, 2019, the British government must make a statement within five days on what it plans to do, according to the European Union (Withdrawal) Act of 2018.

May said this week a ‘no-deal’ Brexit would be better than the EU’s standing offer.

BREXIT - March 29, 2019 at 2300 GMT.

Britain will formally leave the EU. Providing an exit deal is agreed, there will be a transition period during which the bulk of the bloc’s rules and regulations continue to apply while the British government formulates and implements replacement policies on issues such as immigration.

TRANSITION PERIOD ENDS - Dec. 31, 2020

The transition period, designed to ease the impact on businesses and relieve uncertainty, is due to end. Little has been agreed so far about the new arrangements between Britain and the EU on trade, customs and other major issues.