Outgoing European Commission President Jean-Claude Juncker has accused British Prime Minister Boris Johnson of telling “so many lies” during the Brexit campaign.

Mr Juncker, whose term comes to an end in January 2020, added that he was “firmly convinced” the referendum “would go wrong”.

The former Prime Minister of Luxembourg was speaking to German magazine Der Speigel and said he made a £1 gain from the Leave vote in 2016.

He told the publication: “I was one of those early on who was firmly convinced that this referendum would go wrong.

“When then-prime minister David Cameron told me on the sidelines of the 2014 G-20 summit in Brisbane that he really wanted to hold a Brexit referendum, I told him: ‘You’re going to lose it.’

“I made a bet with the European commissioner of British nationality at the time, Jonathan Hill: I get a pound from you if the Remainers lose, you get a euro if you win.

“I have that pound today.”

Britain’s departure from the European Union was initially due to take place on 29 March this year, and was later postponed to 22 May, and 31 October.

A so-called flextension has been granted until 31 January and, since then, a general election has been called for 12 December where Brexit is expected to be a key issue.

Mr Juncker was asked by Der Speigel about why he opted not to fight for a Remain vote and said he had received “many invitations” to campaign.

“Cameron made it clear that he didn’t have any use for me.

“The European Commission is even less popular in Britain than it is on the Continent. I decided not to get involved.

“Looking at it today, I think that was a big mistake. So many lies were told, including by current Prime Minister Boris Johnson, that there needed to be a voice to counter them.”