British Prime Minister Theresa May will hold a special three-hour cabinet meeting Thursday to discuss preparations for a no-deal Brexit.
That means that the European regulation that bans roaming charges will not automatically be part of United Kingdom law, so British mobile operators might be able to reintroduce the charges.
"It also begs the question of how this will be enforced and raises legitimate concerns over lengthy border delays if permits are to be checked".
Barnier tweeted that he had a "useful dialogue" with his British counterpart Dominic Raab on Friday morning about progress their teams had made toward a withdrawal agreement.
Both sides need a broad overall agreement to keep trade flowing between the world's biggest trading bloc and the United Kingdom, home to one of the world's top two financial capitals.
The reports are part of a series of so-called impact papers or risk assessments produced by the British government to prepare its citizens for likely scenarios if the United Kingdom crashed out of the European Union without a deal.More news: United States readies for 'big one' as Hurricane Florence approaches Carolinas
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Their comments came after Mr Raab warned on Thursday that Britain could withhold some of the £39 billion "divorce bill" agreed in December if the there was no overall agreement.
Also like Galileo, the gift that is Brexit will likely mean that contracts with delivery dates that run past the March deadline will also be at risk. They also have a strong incentive to deny the United Kingdom a deal so attractive it might encourage others to follow the British example.
The papers are an attempt to show that Britain is seriously planning for a no-deal Brexit in order to strengthen its negotiating hand with Brussels, although Theresa May has repeatedly said that she would prefer to strike a withdrawal deal with the European Union by November that would than have to be ratified by parliament.
"The fall in the exchange rate would lead to temporarily higher inflation and hence a further squeeze on real wages over the following two to three years, which in turn would weigh on consumer spending and depress growth.' The report added that unemployment would rise, the Treasury would be knocked by lower tax revenue and the United Kingdom could 'fall into recession very quickly".
CBI Director General Carolyn Fairbairn said the government's latest planning papers "make clear firms would be hit with a sledgehammer in the event of no-deal".
Profit at Britain's biggest department stores group, John Lewis Partnership, was wiped out in the first half as it was forced to match discounting by its struggling rivals on a fiercely competitive high street.