British and EU negotiators have reached a deal for Britain to pay between €45bn and €55bn to leave the European Union, the Daily Telegraph has reported.

The newspaper cited two sources saying the agreement was reached at a meeting in Brussels last week, but that the final amount depended "on how each side calculates the output from an agreed methodology".

The Financial Times said Britain had agreed to assume EU liabilities worth up to €100bn, but said net payments over many decades could fall to less than half that amount.

An agreement would be a major breakthrough as Britain prepares for an EU summit in December where it is hoping to get the go-ahead to start the next phase of talks on future trade ties with the EU.

It would leave two major areas on which the two sides still do not agree - expatriate citizens' rights after Brexit and the future of the border.

"The deal on the money is there," a senior source involved in the negotiations told the Telegraph.

"It's now the ECJ (European Court of Justice) question and Northern Ireland that are the outstanding issues ahead of the council," the source said.

One key area of contention is whether the 3.2 million EU citizens living in Britain will continue to be allowed to appeal to ECJ jurisdiction or if their rights will be governed by British courts, as London insists.

Both sides have avoided publicly declaring a clear-cut number for what Britain owes the rest of the EU.

British Prime Minister Theresa May had offered to cover Britain's contributions to its budget in 2019 and 2020 -- a total of around €20bn.

That pledge was reportedly doubled to €40bn at a ministerial meeting in London last week.

A third EU source with knowledge of the talks said the text of the financial agreement would allow a "low figure" to be generated for the British public but would also give the EU the certainty it is looking for.

Asked about the report, a spokesman for Britain's Department for Exiting the European Union said "intensive talks" are taking place in Brussels this week in search of an agreement, but did not address the divorce bill directly.

"We are exploring how we can continue to build on recent momentum in the talks so that together we can move the negotiations on to the next phase and discuss our future partnership," he added.

Another British government official cast doubt on the reported numbers, saying: "I do not recognise this account of the negotiations."

A spokesperson for the European Commission declined to comment.

Mrs May is due to meet President of the European Commission Jean-Claude Juncker and the EU's chief Brexit negotiator Michel Barnier on Monday.

The EU says any British move needs to come by then if leaders at the summit on 14-15 December are to be able to endorse a move to discussions on future trade relations.