The case centred on a local green grocer being prosecuted for selling fruit and vegetables in pounds and ounces, not kilos and grammes.
Steven Thoburn is breaking the law and could face a fine of £5,000.
But the case is not just about the price of bananas on a market stall. European laws stating that fruit and vegetables should not be sold in pounds and ounces by British traders are not valid, a leading constitutional barrister told a landmark legal hearing.
The claim was made in the country's first prosecution of a market trader for refusing to sell fruit and vegetables in metric measurements.
The court case has been billed as British law versus Euro legislation.
Father-of-two Steven Thoburn, 36, is accused of refusing to convert to European-approved measures and sell his goods in kilos and grammes rather than pounds and ounces.
The landmark test case is being brought by Sunderland City Council trading standards department. Mr Thoburn, of Sunderland, denies two counts of having imperial-only weighing scales.
Constitutional barrister Michael Shrimpton, today told a hearing that the 1994 amendment to the Weights and Measures Act of 1985 was not valid.
He said: "The problem arises in this case because we are a member of the European Community and the European Community has a definite policy which is one of compulsory metrification.
"We say the European is entitled to his policies but he is not entitled to say that we in this country apply that principle in defiance of an Act of Parliament.
"Where there is a clash between an Act of Parliament and a regulation of the EC it is the Act of Parliament which takes precedence."
"No one with any concern in this country for the Rule of Law could be other than concerned at a state of affairs whereby a greengrocer should be subjected to coercive actions of the State for selling fruit and vegetables honestly from his stall to customers in pounds and ounces."
Mr Shrimpton said if the amendments had been fully debated then "much of the controversy that has been attached to this prosecution would not have occurred because of the respect we have in this country for the Queen in Parliament and the Rule of Law."
He then described Mr Thubron as an honest trader just wanting to go about his business.
He added: "There is no evidence of deceit or dishonesty in the conduct of this man. He is a man of some courage who has stood his ground in the face of criminal prosecution.
"He is just an ordinary greengrocer who just wants to go about his business of serving customers in the way they want to be served.
"He was simply serving bananas by the pound in fact he was shouting it from his stall.
"The conduct of Mr Thoburn, was open it was there for all to see and at no time was it necessary for undercover purchase to be made."
Barrister Eleanor Sharpston, QC, representing the city council, said the case was not about selling a pound of bananas or forcing the public to buy fruit and vegetables in only metric measurements.
She said the case was not about imposing the will of Brussels by by-passing Parliament. Instead, she told the court the case was about enforcing legitimate law for the protection of the British public.
Miss Sharpston said: "This prosecution is entirely brought to enforce a valid act of Parliament which is the law of the land."
Trading standards officers seized Mr Thoburn's scales from his market stall on July 4, 2000, following the introduction of the European Commission's 1994 Units of Measurements Regulations, which came into effect on January 1 last year.
The hearing was adjourned and is scheduled to last until Wednesday.