UK estimates Brexit bill 'up to 45b euros'

Britain estimates the ultimate cost of meeting its financial obligations to the European Union on Brexit at 40 to 45 billion euros ($A62 to $70.3 billion), a senior UK source says.

"We expect the range to be between 35 and 39 billion pounds," the spokesman said. "We would look at it as a fair settlement of our obligations."

The size of the so-called "divorce bill" emerged after European Commission president Jean-Claude Juncker announced on Friday that he is recommending leaders of the remaining 27 EU states give a green light to the start of trade talks next Thursday.

The breakthrough was hailed by UK Prime Minister Theresa May as "a hard-won agreement in all our interests", while Juncker said it represented "sufficient progress" for negotiations to move on to their second phase.

In dramatic pre-dawn scenes, May and Brexit Secretary David Davis flew to Brussels to confirm with Juncker the text of a joint document setting out proposals on the key divorce issues of citizens' rights, the Irish border and Britain's exit bill.