The UK will pay a financial settlement estimated at £35-£39 billion (40-45 billion euro) as it leaves the EU, a senior British source has revealed.

The size of the so-called "divorce bill" emerged after European Commission president Jean-Claude Juncker announced 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 Prime Minister Theresa May as "a hard-won agreement in all our interests", while European Commission president Jean-Claude Juncker said it represented "sufficient progress" for negotiations to move on to their second phase.

READ MORE: Brexit talks make 'sufficient progress' to move onto second phase of negotiation

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.