Divisions over the UK’s Brexit divorce bill were laid bare on Tuesday as British negotiators pushed back against a mooted €75bn (£66bn) Brexit charge-sheet.
On the second day of detailed 
Brexit negotiations, the British team peppered the Brussels side with questions over how to pay for unwinding 44 years of the UK’s European Union membership.
An earlier session of talks on Monday was so intense officials did not take a coffee break and were running out of water.
Both sides think the mood has improved after the British government admitted last week it had debts to the EU. A statement to parliament on Thursday that the UK has financial obligations from its EU membership helped defuse a potentially toxic row that was brewing, after the foreign secretary, Boris Johnson, said Brussels should “go whistle” for the money.
Michel Barnier, the EU’s chief negotiator, has never put a number on the UK’s exit bill, but estimates have ranged from a €20bn-€100bn gross figure – the €100bn is a gross figure that works out at about €75bn net.
Barnier has told his staff not to talk numbers, the Guardian understands.
EU negotiators think the British government will find it easier to sell the divorce bill to the public by presenting it as the price for a future relationship, according to people close to the talks.
Barnier will not try to pin the British down to a number, when he reports back to EU leaders on whether the British have made “sufficient progress” at a Brussels summit in October.
The final Brexit bill is unlikely to emerge until the last hours of negotiations. Seasoned Brussels negotiators think a deal is most likely to emerge at a late-night summit of EU leaders in the autumn of 2018.
As the talks wound up on Tuesday, some media reported that a “Brussels paper” put the Brexit bill at €70bn. Sources familiar with the negotiations said it was not drawn up by Barnier’s team and had no status in the talks.
Although the British have acknowledged they have debts through 44 years of EU membership, the government has not spelt out what those liabilities are. Neither has the British government published a formal negotiating document on the divorce bill.
But British officials are frustrated at portrayals that is is unprepared. The UK thinks this frequently aired charge does not do justice to the year-long technical preparations at the Department for Exiting the EU (DexEU) and the Treasury.
Negotiators discussed Northern Ireland for several hours on Tuesday morning in a special set of talks led by the EU’s Sabine Weyand and DexEU’s Olly Robbins. British officials described at length their view on the Good Friday agreement and the common travel area.
Both sides say this current round of negotiations is about deepening understanding of the other’s position rather than striking deals.
Three rounds of Brexit talks are scheduled for August, September and October, before an EU summit in late October, when EU leaders will decide whether the UK has made sufficient progress on divorce issues. Only then will the UK be allowed to progress to trade talks.
A European commission spokesman defended David Davis after the Brexit secretary was criticised for spending less than an hour in Brussels to launch the talks on Monday.
Chief negotiators do not have to be present all the time. These are well-structured talks over a week, so work is ongoing and we do not feel concerned about this, said the commission’s chief spokesman.