Brussels says Brexit must happen quickly – however painful it must be

Boris Johnson was already at loggerheads with Brussels within hours of Britain’s historic vote to leave the EU as he claimed there need not be any haste in withdrawing from the bloc, even as European leaders told the UK it must move swiftly to avoid prolonged and damaging uncertainty.

The former Mayor of London, now the favourite to succeed David Cameron as Prime Minister, made the call in a victory speech in central London after Britain voted by 52 per cent to 48 per cent to leave the bloc.

"In voting to leave the EU, it’s vital to stress that there’s no need for haste and, as the Prime Minister has just said, nothing will change in the short term except that work will begin on how to extricate this country from the supranational system. As the Prime Minister has said, there is no need to invoke Article 50," Mr Johnson said.

But following crisis talks, European Commission President Jean-Claude Juncker, European Parliament President Martin Schulz, European Council President Donald Tusk and Dutch Prime Minister Mark Rutte issued a statement saying they expect the UK to initiate its exit “as soon as possible, however painful that process may be”.

“Any delay would unnecessarily prolong uncertainty,” they said.

German Chancellor Angela Merkel, meanwhile, expressed “great regret” at Britain’s decision, but insisted the bloc was “strong enough” to find the “right answers” to the challenges it faces.

Speaking in Berlin, she said the EU had contributed to peace on the continent, but that stability could not be taken for granted.

“The idea of European unification was the idea of peace after centuries of horrendous bloodshed,” she said.

“The founding fathers found a way to come together and it was manifested in the Treaty of Rome almost 60 years ago. For the future, we should not take this for granted.

“We can all see that we are living in a world of turmoil.”

David Cameron said this morning that Article 50 – a procedure that governs how countries leave the EU – would not be invoked before his successor was in place. He said a replacement should be chosen by the Conservative party conference in October.

Estimates for the time it will take to leave the European Union range between two years and seven years.

Meanwhile, group leaders in the EU Parliament have demanded that the UK formally announce its departure and invoke Article 50 immediately.

Guy Verhofstadt, who chairs the liberals, said: “The EU cannot be taken hostage by a Tory leadership wrangle. We need an Article 50 notification now.”

Marcus Weber and Joseph Daul, who head up the European People's Party – the parliament's largest group – said: "There cannot be any special treatment for the United Kingdom. The British people have expressed their wish to leave the EU. Leave means leave. The times of cherry-picking are over.”