Michel Barnier reiterated his gloomy forecast for Britain after Brexit if the country fails to leave the EU with an agreement.
He suggested failing to reach a deal remains a “distinct possibility” just days before the Prime Minister is due to trigger Article 50 and begin Brexit negotiations.
Michel Barnier has offered a gloomy prediction of Britain's future if a Brexit deal cannot be agreed
Writing in the Financial Times, Mr Barnier said: "It goes without saying that a no-deal scenario, while a distinct possibility, would have severe consequences for our people and our economies.
"It would undoubtedly leave the UK worse off.
"Severe disruption to air transport and long queues at the Channel port of Dover are just some of the many examples of the negative consequences of failing to reach a deal.
Who is Michel Barnier? Thu, January 19, 2017
Once dubbed the 'most dangerous man in Europe', Michel Barnier is the Vice President of the European People's Party.
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The veteran French politician has previously served as EU commissioner for internal market and services and also regional policy.
Severe disruption to air transport and long queues at the Channel port of Dover are just some of the many examples of the negative consequences of failing to reach a deal
"Others include the disruption of supply chains, including the suspension of the delivery of nuclear material to the UK.”
He suggested the remaining member states will find it “easier to adjust” to Brexit but urged Britain and Brussels to “reach a deal on the UK's orderly withdrawal from the EU”.
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Mr Barnier has said Britain must 'settle the accounts' before leaving the EU
Mr Barnier added: "It is the only way to properly protect the rights of EU citizens."
On Sunday, Home Secretary Amber Rudd hit back at Mr Barnier’s comments, claiming she “did not recognise” the “apocalyptic” description of Britain without a Brexit deal.
Theresa May is expected to trigger Article 50 on Wednesday
Speaking on The Andrew Marr Show, she said: “I think it’s fair to say I don’t recognise that description… Well, he would say that wouldn’t he. I don’t recognise that apocalyptic description at all.
"I mean let’s face it, the UK Government, the UK economy is doing rather well now, much better than some of us thought previously and the world economy is doing well and the British people are entering into it.
“I think there is a lot of positioning right now.”