Membership of the single market and customs expired at 11pm on Thursday for the UK, four and a half years after the in-out referendum which sought to settle the issue but sparked political turmoil. Now, Mr Barnier has pledged to write about his experiences with the EU negotiating team and the UK side – first led by David Davis, and finally by Lord Frost.
In an interview with French publication Le Figaro, Mr Barnier said: “In the spring I will recount these four extraordinary years in a journal book.”
The book will focus on the fierce last-minute clashes between the UK and EU on their biggest red lines – most notably, fishing.
Sure to be among the pages will be Boris Johnson’s refusal to agree to EU red lines with just hours remaining in negotiations.
The PM responded furiously when told the EU wanted to hit the UK with tariffs if it did not allow them access to British fishing waters with a source adding: “The PM was ready to walk at that point.
“We were writing a script trying to explain to the world we had blown up a £660billion deal over less than a billion quid of fish.”
Mr Barnier admitted this week the most delicate questions centred on in the talks concerned fishing and state aid.
He added: “We have thus spent hours defining in a word the threshold of distortion of competition that one party could create against the other, either by massive State aid in a sector or by deregulation in the environmental, social or fiscal.
“In law, when we qualify damage, it is not the same thing to write “serious”, “material” or “not negligible”.
“For fishing, it was necessary to translate the distribution of quotas on a hundred fish stocks into the annexes to the treaty.”
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Mr Johnson said the EU had provided the UK with a “safe European home” during the 1970s, but the country has now “changed out of all recognition” with global perspectives.
UK’s chief Brexit negotiator Lord David Frost has said “we have a great future before us” as the transition period with the EU came to an end.
He tweeted: “Britain has just become a fully independent country again – deciding our own affairs for ourselves.
“Thank you to everyone who worked with me (and) @BorisJohnson to get us here in the last 18 months.
“We have a great future before us. Now we can build a better country for us all.”