The EU’s chief negotiator Michel Barnier has issued a fresh warning that the UK must accept common standards with the bloc if it wants continued preferential access to European markets.

As the Government prepares to set out its negotiating mandate for forthcoming talks on a post-Brexit trade deal, Mr Barnier said he accepted assurances by Boris Johnson that he did not want to turn Britain into a de-regulated “Singapore-on-Thames”.

However, he said that without agreement on a series of common “ground rules,” efforts to prevent unfair competition and to tackle climate change would be undermined.

Speaking to an ESCP business school seminar in Brussels, he said: “How credible would we be going into the next COP 26 meeting in Glasgow if our future agreement allows businesses to cut corners on environmental and social rights for the sake of gaining market shares?

“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 – who set out the EU’s negotiating mandate on Tuesday – 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.

“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.”

Adrian O’Neill, Irish ambassador to the UK, has said it should be possible to reach agreement on a trade deal by Mr Johnson’s deadline of the end of the year, even if does not cover all aspects of future EU-UK relations.

“I think it will be challenging to negotiate a deal in that timeframe but I think it will be possible. I think Mr Barnier also thinks it will be possible,” he told BBC Radio 5 Live.

“It may not cover all of the desirable areas that we would like it to cover, it may not be as comprehensive as we would have wished, but I think there is sufficient time, certainly, to negotiate a fair trade agreement.”