DEMONSTRATORS waving placards and celebrity supporters packed one of the highest courts in the land yesterday, as leading lawyers and constitutional experts argued over a greengrocers' right to sell bananas by the pound.

Sunderland trader Steven Thoburn, one of the so-called Metric Martyrs, went before the High Court in London to try to win the right to trade in pounds and ounces, despite attempts by the European Commission in Brussels to stop him.

His lawyers warned that making it a criminal offence to sell a pound of bananas in order to please Brussels threatened to cause a "deep constitutional crisis".

Mr Thoburn was found guilty in April and given a 12-month conditional discharge because he had used imperial scales, which did not bear an official stamp, to sell bananas by the pound.

The now infamous bunch of bananas is central to the case.

It was described by counsel for the five Metric Martyrs as the greatest moment in Parliamentary history since the execution of King Charles I, in 1649.

The crowds swelled outside the court as cars tooted support of the cause and 200 protestors waved banners.

Members of the UK Independence Party set up a fruit and vegetables stall selling bananas and sprouts in imperial measures.

Actor Edward Fox added his weight to the protest, saying: "I am here simply as a supporter of the Metric Martyrs' cause. I believe it is such an important issue for the people of Britain."

Two judges were asked to rule that the 1985 Weights and Measures Act, introduced after Britain joined the European Community, provided a loophole which meant EU directives requiring goods to be sold in metric units did not apply in England and Wales.

Michael Shrimpton, appearing for the five, said: "It is a test case of constitutional importance, we say, and the public and the country are entitled to know what has been done in their name."

Mr Shrimpton said none of the five had refused to serve goods in metric measures.

If asked to serve in metric, they would, the court heard. But they also wanted the constitutional freedom to serve in imperial measures.

He told the court that, if the various local authorities defending the ban on selling goods solely in pounds and ounces succeeded in defeating their challenge "the damage which will be done to the fabric of the constitution will be awesome".

The hearing continues tomorrow and is expected to last about three days.