The UK will have to pay a bill of about £50 billion (€58 billion) when it leaves the EU, European Commission president Jean-Claude Juncker has warned.

While there is no desire to “punish” Britain for leaving the bloc, the EU must prevent other countries from following, the head of the EU’s executive arm told the BBC in an interview broadcast on Friday.

“We have to calculate scientifically what the British commitments were and then the bill has to be paid,” he said. Asked if the bill will be £50 billion, Mr Juncker replied: “It’s around that.”

The size of Britain’s exit bill will be among the first - and most contentious - topics for discussion, with British ministers indicating they do not believe the UK is liable for such a large sum.

This is the clearest indication from the commission of the size of the bill, and is in line with an estimate cited by Austrian Chancellor Christian Kern of €60 billion.

Mr Juncker also said Brexit was “a failure and a tragedy”. The EU’s most senior civil servant promised that Brussels will approach the negotiation of Britain’s withdrawal in a “friendly” and “fair” way, but warned that European institutions were not “naive” about the process.

He said: “It will be a bill reflecting former commitments by the British Government and by the British Parliament.

“There will be no sanctions, no punishment, nothing of that kind.”

Prime Minister Theresa May is due formally to notify Brussels of Britain’s intention to leave the EU in a letter to the European Council on March 29th - just four days after the EU’s 60th anniversary celebrations in Rome on Saturday.

The letter will set in train a two-year process of negotiation leading to the reduction of the EU from 28 to 27 members on March 29th, 2019.

Asked how he felt about Brexit, Mr Juncker said: “It is a failure and a tragedy.

“I will be sad, as I was sad when the vote in the referendum took place in Britain. For me, it is a tragedy.

“I am anything but in a hostile mood when it comes to Britain. We will negotiate in a friendly way, a fair way, and we are not naive.”

Mr Juncker made clear he places high priority on protecting the status of the three million EU nationals resident in the UK and the one million Britons living on the continent.

“I am strongly committed to preserving the rights of Europeans living in Britain and British people living on the European continent,” he said.

“This is not about bargaining, this is about respecting human dignity.”

-Press Association