The EU’s chief negotiator will stay in London until Wednesday to continue post-Brexit trade talks with his UK counterpart, EU sources say.
Michel Barnier arrived in the UK on Thursday to restart negotiations after they stalled, and he was due to return home on Sunday.
EU sources told the BBC more talks are also planned in Brussels from Thursday.
Northern Ireland Secretary Brandon Lewis said he was hopeful of a “positive outcome” from negotiations.
But he told Sky’s Sophy Ridge that the UK would be “ready as a country for whatever happens”, with Brexit providing “big opportunities for us”.
The UK left the EU on 31 January but has been in a so-called transition period – continuing to follow EU rules and pay into the bloc – while the two sides hammer out a post-Brexit trade agreement.
The transition period is due to end on 31 December, but if a deal is not reached, the UK will trade with the EU on World Trade Organisation rules.
Some critics fear a no-deal scenario will cause problems for businesses, but the government insists the UK will prosper.
The EU had said a deal needed to be agreed by the end of October to allow time for it to be ratified by all the relevant parliaments, but UK Prime Minister Boris Johnson had warned of walking away from talks on 15 October.
After strong words from both sides and calls for “fundamental changes” to the approach to negotiations, a return to the table was agreed and Mr Barnier has been holding talks with UK chief negotiator Lord David Frost since Thursday.
On his arrival, Mr Barnier told reporters “every day counts” and the two sides shared a “huge common responsibility” in the talks.
The discussions had been expected to wrap up later on Sunday with the possibility of consequent conversations, but EU sources have told the BBC they will now continue in London for three more days, before moving to Brussels.
In line with a demand made by the UK, the talks resumed on all subjects based on proposed legal texts prepared by officials.
They also said that “nothing is agreed” until progress has been reached in all areas – which has been a key demand of the EU.