Stefaan De Rynck, who is part of Mr Barnier's negotiating team said that Brexit was a “lose-lose” situation. 

Speaking at a speech at Chatham House in London today, Mr De Rynck claimed that Brexit would never be labelled as a “success”. 

He said: “I don’t think we’ll ever label Brexit a success in the EU. 

“It’s a mutual weakening of the two parties.

“Economically for us, Brexit is a lose-lose situation… how do we minimise losses economically on both sides?

“No matter how you turn Brexit it means there will be barriers where they don’t exist today no matter how ambitious the free trade agreement could be.”

Mr De Rynck also said that the European Union fears Britain may not keep its word on certain post-Brexit agreements. 

The chief claimed that simple trust between the UK and Brussels was “not enough” and more “glue” was needed in talks.

“What worries people on European Union side is the idea the UK will leave the single market and we’d have to trust somehow that outcome would be same on UK side in terms of standard setting,” he said.

“That’s not enough glue to keep the system together, that trust.”

Mr De Rynck added that more than trust was necessary to ensure a “level playing field” after Brexit. 

The EU official also praised the progress made by both sides in discussions so far as the UK moved through the first stage of talks. 

“We have reached sufficient progress but that is not full progress on all issues,” he said.

Trade talks are expected to begin in the new year after the Prime Minister came to an agreement in Brussels. 

The EU has issued a three-page document outlining its harsh guidelines for negotiating the future relationship with Britain, insisting the final deal can only be “concluded once the UK has become a third country”.