NEVER before has so much attention been focused on a simple bunch of bananas. In fact they became, in the words of a district judge yesterday, probably the most famous bunch of bananas in legal history.

At 25p a pound, the sale of the fruit on imperial scales, in defiance of the law, has seen the sharpest legal minds pitted against each other over matters of constitutional importance.

And it saw the advent of the Metric Martyrs, personified by Sunderland greengrocer Steve Thoburn, who became a reluctant standard bearer for an anti-Euro cause.

Of Byzantine complexity, the landmark trial reached its conclusion yesterday with the conviction of Thoburn for two offences of breaching the Weights and Measures Act 1985.

The facts were never in dispute. For campaigners, what it hinged on was whether the European law or British law took precedence. The trial had its genesis in a visit by trading standards officers to Thoburn's stall in Southwick in February last year, when he was warned about using imperial scales.

After officials stamped his scales and banned them from use, he defied them and an undercover officer moved in to buy 54p worth of bananas - weighed on imperial scales. Quick to spot an opportunity, the UK Independence Party, whose central aim is the UK's withdrawal from the EU, rallied around the Metric Martyr banner.

Thoburn was backed, too, by an unlikely gathering of celebrities, including Joanne Rowling, of Harry Potter fame, Sir Patrick Moore and Sir Ranulph Fiennes. They were among 40 writers, sportsmen and actors who became honorary members of the British Weights and Measures Association, leading his defence. The first day of a the trial opened with banana-brandishing protestors outside Sunderland Magistrates Court - encouraged by hooting cars. But inside, the council's barrister, Eleanor Sharpston QC, argued the case had nothing at all to do with selling a pound of bananas.

Under a 1994 EU directive, it was perfectly permissible to have equipment which measured in pounds and metric. Neither was there a case about imposing the will of Brussels by by-passing Parliament, because Parliament had already given a responsible minister the powers to do what he had done.

Rather, it was about avoiding consumer confusion, the situation where a housewife with two kids had to do mental arithmetic to work out whether apples priced in Sainbury's in metric were cheaper than those sold on Thoburn's imperial scales.

And it was about promoting fair competition. Where other law-abiding traders had already turned to metric, by using imperial scales, Thoburn's goods appeared cheaper than his competitors.

Miss Sharpston said: "In 1973, we joined the EC club. As long as we remain members of that club, we must play by the rules of that club."

Constitutional barrister Eric Shrimpton, who described himself as a "humble polyester", made up for any lack in silk with a scintillating display of legal gymnastics. At the heart of his argument was the fact that no European legislation could override an Act of Parliament.

He said: "No one, with any concern in this country for the rule of law, can be other than concerned at a state of affairs whereby a greengrocer should be subject to the coercive action of the state for the sale of his fruit and vegetables from his stall honestly, to customers, in pounds and ounces."

Mr Shrimpton said there had been no debate at all in Parliament about the amendment of the Weights and Measures Act, or the principles of compulsory metrification.

Had this been done by Parliament with primary legislation, this change would have carried the powers of the sovereign and would have been constitutionally legitimate.

In an eloquent peroration, he said: "This is a case which strikes at the very heart of British life. Weights and measures are part and parcel of our way of life, the way we act, the way we think, and the way we feel and have been for generation upon generation.

'They are part of the customary way of life which, under international law, we are entitled to respect. European law violates our right for self determination, we have fought three wars this century for the right for self determination."

The point of law was argued for three days between Thoburn's team of a barrister, two solicitors, and the local authority's team of two barristers and three solicitors.

Judge Bruce Morgan decried the complexity of the law which required the prosecution to take him through a "Byzantine" maze of cases.

Reference was made to, not only the Weights and Measures Act, but to 89 reported cases going back to 1661, six treaties and conventions, 16 acts of Parliament, and 21 directives and statutory instruments. And all this for a "single bunch of bananas".

Addressing the many constitutional milestones in Britain, as outlined by Mr Shrimpton, Mr Morgan said: "Constitutional law is not like a stagnant pond. It is like a fresh stream constantly changing, as it does constantly change the surrounding landscape, in order to meet the needs of the time."

Ruling in favour of Miss Sharpston's arguments, he pointed out that Britain had not been coerced into joining Europe, but had done so voluntarily. As for that bunch of bananas, we will still be hearing much more of it as the saga continues up the legal ladder.

He said: "From the moment the Rt Hon Edward Heath signed the treaty on behalf of the United Kingdom, he also agreed to the eventual demise of the imperial system. Until this case, I am not aware of anyone seeking to challenge Parliament in relation to that. This country has decided its political future lies in Europe and the European Union. As such it has joined the European club and by doing so has agreed to be bound by the rules and regulations of that club."