BRUSSELS (Reuters) - The European Union will next month demand Britain agree to pay a fixed percentage of the EU’s outstanding obligations on the day it leaves the bloc, in defiance of a British rejection of that logic as “preposterous”.

A traffic sign is seen in front of European and Union flags in London, Britain, March 20, 2017. REUTERS/Stefan Wermuth

A draft EU negotiating paper, seen by Reuters, that will be put to London when Brexit talks begin following a national election in Britain on June 8 makes clear that suggestions from Prime Minister Theresa May’s government that the Union might end up owing rather than getting money cut no ice in Brussels.

The paper on principles of the financial settlement that the EU wants from London on departure in March 2019 sets no figure, and chief negotiator Michel Barnier has made clear it cannot be calculated until the end as it depends on the EU’s spending.

However, he wants an agreement on how the “Brexit bill” will be calculated, perhaps by late this year, before the Europeans agree to launch talks that May wants on a free trade agreement.

EU chief executive Jean-Claude Juncker has said Britain may have to pay its 27 allies some 60 billion euros on departure and some experts estimated the up-front cost, before later refunds, could be nearly double that -- suggestions May’s foreign minister Boris Johnson called “absolutely preposterous”.

The paper to be discussed among diplomats next week before Barnier presents the opening demands to London in the week of June 19, spells out that while Britain will get some credit -- notably its 39 billion-euro share of the capital of the European Investment Bank.

But the list of what it must pay, and go paying for some years after Brexit, is much longer.

Four pages of appendix details list more than 70 EU bodies and funds to which Britain has committed payment in a budget set out to 2020.

Yet the three-page main document made no mention of Britain getting credit for a share of, say, EU buildings, as British ministers have said it should have. EU officials argue Britain was not asked to pay extra for existing infrastructure in Brussels when it first joined the bloc in 1973.

Among obligations Britain will be asked to cover are the funding until summer 2021 of British teachers seconded to schools catering to the EU’s staff and diplomats.

Other payments include promises to fund Syrian refugees in Turkey, aid for the Central African Republic, the EU aviation safety agency and the European Institute for Gender Equality.

“The United Kingdom obligations should be fixed as a percentage of the EU obligations calculated at the date of withdrawal in accordance with a methodology to be agreed in the first phase of the negotiations,” the paper states.

It adds that people, businesses and organisations in Britain would continue to benefit from some EU funds for some time after Brexit.

Britain has about 13 percent of the EU’s 507 million population and accounts for some 16 percent of its economy. Its net contribution to the EU’s 140 billion-euro annual budget has typically been roughly 10 billion euros in recent years.