Britain’s global reputation has been damaged and lawyers have been left “incredulous” by the Government’s plan to override key elements of the Brexit deal, Sir John Major has said.

The Conservative former prime minister lambasted the controversial move by Boris Johnson, describing it as “unprecedented in all our history – and for good reason”.

Sir John said the UK Internal Market Bill, which ministers have admitted will breach international law, had “damaged our reputation around the world”.

“Lawyers everywhere are incredulous that the UK – often seen as the very cradle of the Rule of Law – could give themselves the power to break the law,” he said in a pre-recorded lecture to Middle Temple on Monday evening.

“Moreover, at a moment when we need to maximise our commercial activities, this Bill has had a corrosive impact on the reputation of English and Welsh jurisdiction.

“This may have a practical cost. International dispute resolution can be conducted anywhere overseas and the Bill could erode the present pre-eminent position of the UK and, perhaps, especially London.

“Was this considered when the Bill was drafted? Was there consultation with the legal profession? If not, why not? And if there was consultation, why was it ignored?”

The House of Lords is expected to vote on the Bill later on Monday, with the Government facing a potential defeat at the hands of peers outraged by its powers.

Sir John and all living former prime ministers have previously criticised the legislation.

In recent decades, we have consoled ourselves that we 'punch above our weight' in international affairs. I think that was true - but that was then and this is now

He also warned in his speech that Britain is “no longer a great power” and “will never be so again”.

The former prime minister, who was a vocal supporter of the Remain campaign in the 2016 referendum, said: “In a world of nearly eight billion people, well under 1% are British.

“We are a top second-rank power but, over the next half century, however well we perform, our small size and population makes it likely we will be passed by the growth of other, far larger countries.

“In recent decades, we have consoled ourselves that we ‘punch above our weight’ in international affairs. I think that was true – but that was then and this is now.

“Our hefty international influence rested on our history and reputation, buttressed by our membership of the European Union and our close alliance with the United States.

“Suddenly, we are no longer an irreplaceable bridge between Europe and America. We are now less relevant to them both.”