Earlier this month, Mr Johnson said "early progress" on agreements over financial services and personal data protection would be "a test of the constructive nature of the negotiating process".

But pledges in the political declaration to reach an agreement on financial services by June 2020, and on data by the end of December, were dropped by Brussels when the EU's negotiating mandate was published.

Government sources said that meant Mr Johnson was fully entitled to ignore elements of the political declaration. Britain will refuse to sign up to EU rules on state aid, and will not build any infrastructure to deal with customs declarations on goods crossing from the mainland to Northern Ireland despite EU demands that they must exist.

Mr Barnier said: "We are ready to offer to the UK super-preferential access to our markets – a level of access that would be unprecedented for a third country.

"Is this something we can do without firm guarantees that the UK will respect the 'level playing field' and avoid unfair competitive advantages? The answer, I'm afraid, is simple. We cannot. We want competition in the future but it must be fair – fair and free."

Mr Barnier said that, whatever the outcome of the trade talks, there would be checks on goods entering the EU from Britain from the beginning of 2021 when the current transition period ends.

He said: "Of course we love 'Made in Britain' but we must guarantee that the goods we import from the UK, tariff and quota free, really are British.

"We cannot take the risk that the UK becomes a kind of assembly hub for goods from all over the world, allowing them to enter the single market as British goods."