STRASBOURG, France (AFP) - European Commission head Jean-Claude Juncker has sharply criticised politicians Nigel Farage and Boris Johnson as the "sad heroes" of Brexit who backed out of leading Britain through the EU exit they had campaigned for.

"The Brexit heroes of yesterday are now the sad heroes of today," Juncker told a session of the European Parliament in Strasbourg, France.

"Those who have contributed to the situation in the UK have resigned, Johnson, Farage and others. They are as it were retro-nationalists, they are not patriots," Juncker said.

"Patriots don't resign when things get difficult, they stay," he added.

Mr Juncker was reporting to MEPs the results of last week's historic EU summit, in which British Prime Minister David Cameron reported to his fellow leaders the vote by Britain to leave the bloc.

Mr Johnson pulled out of the leadership race to succeed Mr Cameron, who has said he will resign by October, while Mr Farage on Monday stepped down as leader of the eurosceptic UK Independence Party.

Mr Juncker also criticised those who campaigned to leave the EU for failing to know what they wanted to do next, with Britain delaying on pulling the trigger on its official divorce from the EU.

"Instead of developing a plan, they are leaving the boat," Mr Juncker said.

EU president Donald Tusk meanwhile said the bloc's members "hope to have the UK as a close partner in future", but reiterated that it would have to accept the union's free movement rules if it wanted access to the single market.

"We will not sell off our freedoms and there will be no single market a la carte," he told MEPs.

Senior liberal MEP Guy Verhofstadt also slammed Mr Farage and Mr Johnson.

"Brexiteers remind me of rats leaving the sinking ship," said Mr Verhofstadt. "What are you waiting for - the next referendum in France, in Italy maybe."