"There can be no sector by sector participation in the single market", he said. One former Labour Cabinet minister told me: "the idea is to do get a transitional phase that goes on for 5 years or so and then we just decide to stay in it".
He also poured cold water over moves by the City and the vehicle industry to cut special deals to remain in the free market.
"I have heard some people in the United Kingdom argue that one can leave the single market and keep all of its benefits - that is not possible", he said. He continued, "I have heard some people in the United Kingdom argue that one can leave the single market and keep all of its benefits".
The City of London sent a delegation to Brussels to discuss a post-Brexit free trade deal for financial services.
Mr Barnier also claimed that businesses in the United Kingdom could face additional red tape - and exports of live animals and animal produce would be subject to MORE border checks. It would also involve shared regulatory supervision and joint dispute resolution.
It is not the first time Barnier has made plain he thinks the British have misunderstood the reality of Brexit.
He said in that scenario business would fall back on World Trade Organisation rules that would include duty of nearly 10% on vehicle imports and around 19% on alcohol.
He also said that British manufacturers that export to the European Union would face increased transport costs because they would have to keep their products in stock for 3 or 4 days instead of a few hours, and rent warehouse space.
Britain and the European Union must avoid a no deal situationMr Barnier added that failure to reach a Brexit trade deal would mean "a return to the distant past", with trade regulated by World Trade Organisation rules which would impose tariffs on goods. "And the United Kingdom would have even more to lose than its partners". The prime minister has still to renege on that as United Kingdom officials argue a threat to walk away from the talks without an agreement should help prevent the European Union from demanding too much of it.
He pointed out that access to the internal market without the customs union, as happens in the European Economic Area, still requires EEA members Norway, Iceland and Liechtenstein to comply with a system of procedures and customs controls; similarly, Turkey's customs agreement with the EU, without access to the internal market, has an implied system of procedures and customs controls as well.