Published: 1:07 PM July 16, 2019 Updated: 6:02 PM September 17, 2020

Outgoing European commission president Jean Claude-Juncker has admitted one of his biggest regrets was listening to David Cameron during the EU referendum campaign.

Despite it being Cameron's wishes not to have the European Union involved in the weeks leading up to Britain voting in the referendum, Juncker has said it was a "failure of duty" on their part not to have participated to respond to claims made about the organisation.

He told told Japanese newspaper Asahi Shimbun: "David Cameron, the then British prime minister, did not want to have us interfering in the referendum campaign.

"I agreed that we should not interfere but that was a major mistake."

He said that he wished he had hit back at the "lies" told by the Brexiteers throughout the campaign - which would have included the £350m bus claim and the suggestion Turkey was joining the EU - peddled by both Leave camps.

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He continued: "Because of all the lies which have been told to people during this referendum campaign, it would have been wise to have one institution to say 'this is a lie.'

"We did not do that, and we were failing to do our duties."

Juncker also insisted that the European Union will not renegotiate with the United Kingdom, despite claims from Boris Johnson, Jeremy Hunt and even Jeremy Corbyn.

"We will not renegotiate the withdrawal agreement.

"We can give some clarifications on the political declaration related to the future relations but as far as the substance is concerned, there will be no renegotiation.

"This is not an agreement between Theresa May and myself, this is a treaty between Britain and the EU."

The favourite to succeed Juncker, Ursula von der Leyen, has already been praised for issuing a rebuke of Nigel Farage in the European parliament, by telling him that the parliament "can do without you".