European Council president Donald Tusk is to meet Prime Minister Theresa May in Downing Street for Brexit talks on Thursday, his spokesman has said.
The summit is billed as "discussing the way ahead on Brexit" after the PM formally triggered two years of withdrawal talks when she invoked Article 50 of the Lisbon Treaty last week.
Mr Tusk has made it clear he is seeking a fair settlement, but warned the Brexit negotiations could become confrontational at times.
The meeting comes after Mrs May appeared to relax her stance on free movement of labour after Brexit by signalling that curbs would not be imposed in the immediate aftermath of withdrawal.
The Prime Minister said there would be an "implementation" phase once a deal had been hammered out, with businesses and governments needing a "period of time" to adjust to the new rules.
Mr Tusk has indicated that post-Brexit trade deal talks could begin this autumn, but only if "sufficient progress" has been achieved in negotiations on the arrangements for Britain's withdrawal - widely seen as a reference to agreement on a "divorce bill" of an estimated £50 billion set to be presented to the UK.
The European Council president predicted that withdrawal negotiations would be "difficult, complex and sometimes even confrontational".
Mrs May has said that by Brexit Day in March 2019 she expects the shape of a new UK-EU trade relationship to be clear, but appeared to accept that the formal conclusion of any agreement will have to wait until after withdrawal.
This followed a warning by Mr Tusk, set out in draft guidelines for negotiations, that EU rules state trade deals can only be done with non-members, so the most the UK can hope for prior to Brexit is an "overall understanding on the framework for the future relationship".