TWO leading figures in the Scottish Green Party, one a candidate in the Scottish Parliament elections, were arrested yesterday when trouble flared at one of the largest protests in Scotland against genetically-modified crops.

Four other people were also detained in scuffles with police officers as some of the 100 or so demonstrators, demanding an end to GM crop trial sites, spilled over fencing and invaded a Midlothian field.

Extensive damage was caused to the field, a test site of the Scottish Agricultural College at Boghall Farm on the outskirts of Edinburgh.

Demonstrators tore at the earth as they staged a sit-in and police officers, some with dogs, moved in as the trouble began shortly after a cardboard ''coffin'' was thrown into the field.

Several clashes erupted in what had initially been a good-natured show of opposition by the pressure group, Earth First.

One man had to be carried, handcuffed, by four officers to a police van.

Lothian and Borders police, which at the height of the trouble had around 30 officers at the scene including reinforcements, said later six protesters had been arrested.

The six, four men and two women, are expected to face charges including vandalism and breach of the peace.

Scottish Green Party candidate Mark Ballard, on the Lothian list for the May election, said later he had been arrested for pulling up genetically modified oil seed rape. He claimed that if the Government refused to protect people and the countryside his party had to take ''peaceful direct action''.

Mr James Mackenzie, the party's education spokesman, said after his arrest that to test how dangerous genetically modified crops were by releasing them into the environment was ''irresponsible in the extreme''.

Yesterday's ''Stop the Crop'', protest which began with a march from a nearby organic farm, is the latest in a series of demonstrations on the issue of the so-called ''Frankenstein foods''.

It came exactly a year after 60 activists from Fife Earth First attacked a crop of genetic oilseed rape growing in Fife.

The protest also took place on the eve of a court trial in Plymouth where two women face charges in connection with an incident where #60,000 of damage was caused at a controversial test site of GM maize in Devon.

On Saturday in the south, activists from the group Genetix Snowball stole 100 items of GM food to ''decontaminate'' a Tesco supermarket in London and carried out similar action at a Manchester Safeway store.

The amount of damage caused yesterday in Midlothian is not yet known. Protest organisers said ''genetic pollution'' would not be tolerated. They claimed the health risks were unknown yet the politicians and regulatory systems were failing to protect the interests of the public.

Mr David Cranstoun, a specialist with the Scottish Agricultural College, said there was one trial site at Boghall on genetically modified winter oilseed rape while another dealing with spring oilseed rape was planned shortly.

He stressed the trials, part of the UK variety testing system, were not carried out ''for Monsanto or for any other potential seller of GM material''.

Mr Cranstoun added that, as a result of the trials, the authorities would decide whether crop varieties - both conventional and genetically-modified - would be marketed in the UK.

The SAC believed the way to overcome the confusion and anxiety over the materials was to carry out controlled trials.

''There are those who wish to destroy the trials here,'' Mr Cranstoun said. ''If they succeed, there will be less evidence available on which good objective decisions can be taken in the future.''