Britain’s exit from the EU is a "waste of time and energy", the European Parliament’s chief Brexit co-ordinator has said.
Guy Verhofstadt insisted he respected the outcome of the referendum but quitting the bloc was a "very negative project".
However, the shock move has fuelled a resurgence in the popularity of the union on the continent, the former prime minister of Belgium claimed.
In a speech at the London School of Economics and Political Science (LSE), he said the decision had "opened people’s eyes" and the predictions other countries would follow have died away.
He said: "I continue to believe that Brexit is a very negative project, that it is, in fact, a waste of time and energy.
"The destruction of a strong political bond that made people on both sides of the Channel richer, freer than ever before."
Mr Verhofstadt said he hoped the EU and UK could establish a new relationship that "hopefully will be beneficial for everybody".
He added: "Since Brexit I see that the mood has reversed, in a certain way the European Union regained popularity.
"People are less critical now of the union but they want to reform Europe, not to leave Europe, not to destroy it."
Mocking Theresa May’s political frailty as speculation about her future continues, Mr Verhofstadt joked the Prime Minister had chosen to make her speech on Brexit in Florence because she felt at home in a city with a history of political plotting and back-stabbing.