Updated | EU negotiator denies Brexit bill 'punishment'

The EU's chief Brexit negotiator Michel Barnier insisted Wednesday the bloc was not punishing Britain as London firmly rejected a reported €100 billion exit bill.

Barnier warned however against the "illusion" that leaving the European Union would be quick or 'painless', urging Britain to start talks as soon as possible after its general election in June.

“Some have created the illusion that Brexit will have no material impact on our lives and that it will be painless. This is not the case,” he told a news conference as he unveiled his proposed negotiating mandate for two years of talks, before adding that it was not the European Commission’s intention to “punish” Britain for leaving the bloc.

"There is no punishment, there is no Brexit bill. The financial settlement is only about settling the accounts," Barnier said.

Over the past month, the 27 other member states have drafted negotiating guidelines for the executive Commission that leaders agreed on Saturday. In the course of drafting, governments insisted on clarifying that Britain be made to pay up front for, among other things, contingent liabilities for guarantees on loans made by, for example, the European Investment Bank.

Barnier has repeatedly said that the final amount cannot be calculated until Britain is leaving, since the EU budget will change. However, EU leaders want agreement on the "methodology" for the calculation among several conditions for opening the talks on a future free trade deal that Britain is seeking. Leaders hope that agreement could be reached by December.

Hours before Barnier was due to speak, a Financial Times headline saying the EU might seek an upfront payment in 2019 of up to €100 billion, drew an immediate rejection from Britain's Brexit Secretary David Davis that he would pay that sum.

The European Commission has previously given a ballpark estimate of the bill of about €60 billion. The Financial Times said the calculations it referred to would result in a net payment from Britain of roughly that level, after subsequent reimbursements.

Davis said his country could simply walk away from the negotiations. "We will not be paying 100 billion," he told British media. "In the walk-away circumstance there is nothing to be paid," he said.

UK Prime Minister Theresa May has warned that she would rather Britain exit the EU without any agreement on future ties than accept a "bad deal". But May was put on the defensive this week after leaks about a disastrous dinner in London with European Commission President Jean-Claude Juncker and Barnier.

The leaders of the other 27 EU nations on Saturday unanimously agreed a tough set of guidelines for the talks with Britain, covering issues of money, the rights of EU citizens, and the border in Northern Ireland.

Publishing his Brexit mandate, Barnier said the EU would "put all its efforts" into reaching a deal but said negotiations must start as soon as possible after "ten months of uncertainty" and suggested the outcome of June's general election would not change anything.