Brussels (AFP) - Nigel Farage, leader of the anti-EU UK Independence Party, on Tuesday told a jeering European Parliament he had had the last laugh after Britain defied their warnings and voted to quit the EU.

"Isn't it funny? When I came here 17 years ago and I said I wanted to lead a campaign to get Britain to leave the EU, you all laughed at me but you are not laughing now," Farage told MEPs.

Farage said the European Union was "in denial" about its failing and wrong-headed ambitions for a united Europe from which voters were turning away in droves.

"You have imposed on them a political union and when the people in 2005 in the Netherlands and in France voted against you, you simply ignored them and brought the Lisbon Treaty in by the back door!" he told MEPs in an emergency debate on Britain's Brexit vote.

Going into the chamber, a beaming Farage embraced European Commission head Jean-Claude Juncker, his long-time sparring partner who in his own address asked why the UKIP leader had even bothered to turn up.

But Farage would not be denied his moment, saying Thursday's vote was "seismic" with far-reaching implications beyond Britain's immediate future.

"The little people rejected the multinational companies, the banks, the big politicians and they said: 'we want our country back,'" Farage said.

"The United Kingdom will not be the last member state to leave the European Union!"

Farage also berated MEPs as being out of touch with the real world -- "I know most of you have never had a proper job" -- and told they were mistaken if they believed it right to punish Britain.

- 'Best friends'? -

Britain and the EU were hugely important trade partners and if the bloc threatened that, then the EU would be the loser with hundreds of thousands of jobs at stake, he said.

But if the two sides reached a "sensible" trade deal then Europe would see "that the UK will be your friend, your best friends in the world."

The immediate question is when Prime Minister David Cameron will trigger Article 50 of the Lisbon Treaty to start the exit negotiations.

Cameron, in Brussels for what promises to be a difficult summit with his EU peers, has said that this decision must wait until his successor is in place, likely in September.

MEPs at the end of the emergency session passed a resolution saying the negotiations should begin as soon as possible.