The EU and UK have agreed a draft agreement on their future relationship, paving the way for a Brexit deal to be finalised this weekend.
The political declaration – outlining how trade, security and other issues will work – has been “agreed in principle”, the European Council says.
London and Brussels have already agreed the draft terms of the UK’s exit from the EU on 29 March 2019.
Theresa May will make a statement to MPs at 15:00 GMT.
Downing Street said the prime minister has briefed cabinet ministers on the draft agreement in a conference call.
Last week, the UK and the EU agreed a 585-page legally-binding withdrawal agreement, covering the UK’s £39bn “divorce bill”, citizens’ rights after Brexit and the thorny issue of the Northern Ireland “backstop” – how to keep the border open if trade talks stall.
The political declaration is a separate, far shorter document, setting out broad aspirations for the kind of relationship the UK and the EU will have after Brexit, and is not legally-binding. Some of the wording of it is non-committal and allows both sides to keep their options open.
European Council President Donald Tusk said in a tweet: “I have just sent to EU27 a draft Political Declaration on the Future Relationship between EU and UK. The Commission President has informed me that it has been agreed at negotiators’ level and agreed in principle at political level, subject to the endorsement of the leaders.”
It follows a meeting in Brussels on Wednesday evening between Mrs May and European Commission president Jean-Claude Juncker.
Downing Street said Mrs May will return to Brussels on Saturday for further talks with Mr Juncker, on “how we can bring to a conclusion this process in the interest of all of our people”.
“No final deal can be agreed without the approval of the European Council on Sunday,” said the prime minister’s official spokesman.
Tensions remain over some parts of the withdrawal agreement.
Spain’s prime minister, Pedro Sanchez, has said his government is “annoyed” that the divorce agreement does not specify that Gibraltar’s future must be decided directly by officials in Madrid and London – and France is understood to have sought amendments to the wording on fishing rights in UK waters.
If the withdrawal agreement and the political declaration are signed off on Sunday, Theresa May will then turn her attention to getting the deal through the UK Parliament, where there is not thought to currently be a majority in favour of it.
The BBC’s Brussels reporter Adam Fleming said, from a first reading of the draft document that has just been published, it contained “something for everyone” but there was “lots” in it that would need to be negotiated after Brexit day.
1st reading of draft Political Declaration:
1⃣something for everyone – ease of trade v level playing field, customs v independent trade policy, close but no 4 freedoms
2⃣maintenance of many existing security capabilities
3⃣LOTS to negotiate after 29/3
— Adam Fleming (@adamfleming) November 22, 2018
If all goes as planned, the UK and the EU will use the political declaration as the basis for a trade agreement, to be hammered out during a 21-month transition period that is due to kick-in after 29 March, during which the UK will continue to be a member of the EU single market and customs union.
The draft document stresses that any final deal with the UK must not interfere with the EU’s “four freedoms” – the free movement of goods, services, capital and people within the remaining 27 EU nations.
It says: “The future relationship will be based on a balance of rights and obligations, taking into account the principles of each party.
“This balance must ensure the autonomy of the union’s decision-making and be consistent with the union’s principles, in particular with respect to the integrity of the single market and the customs union and the indivisibility of the four freedoms.
“It must also ensure the sovereignty of the United Kingdom and the protection of its internal market, while respecting the result of the 2016 referendum including with regard to the development of its independent trade policy and the ending of free movement of people between the Union and the United Kingdom.”
Commons leader Andrea Leadsom, one of a group of Brexiteer cabinet minister reported to have been pushing for changes to the agreement, urged MPs to back it.
She said: “Once the deal is agreed it will be put to Parliament and MPs will have the decision on whether to back it or reject it.
“But people should not be under any illusion the EU would be prepared to start all over again and negotiate a different deal.
“So it’s very important that we do end up with a straightforward approval of the deal.”
Labour and the other UK opposition parties have said they will vote against the withdrawal agreement – as have Mrs May’s partners the Democratic Unionist Party, who she relies on to keep her in power.
Dozens of her own Conservative MPs are also against it, arguing that it will keep the UK tied too closely to the EU and is not a “proper” Brexit.