TWENTY people were arrested in Edinburgh yesterday when ''Eco warriors'', claiming to be waging a campaign against the city's rising car use, clashed with the police.

More than 150 protesters, including nine members of the cast of the Fringe production ''Road Rage'', brought the Grassmarket, one of Edinburgh's most popular spots for visitors, to a standstill in a publicity stunt that backfired when violence erupted.

The event had originally been planned as a '' photocall'' by members of the cast of the Fringe production, a play at the nearby Gilded Balloon venue about the life of a roads protester.

However, real-life eco-protesters ''Reclaim the Streets'' which claims to be a worldwide movement ''to give cities back to people'' organised a march from the Mound to the Grassmarket without applying for police permission and brought traffic chaos.

As the procession made its way up to the High Street and on to King George IV Bridge, jostling broke out as mounted police tried to contain the demonstration.

The protesters then marched into the Grassmarket where music and dancing got under way .

One man sat 15 feet in the air in a makeshift scaffolding pyramid close to a thoroughfare often used by emergency vehicles. More police were called in as demonstrators later lay in the middle of the road and refused to move.

Lothian and Borders police said the 20 arrested had been charged with a variety of public order offences and would be appearing at the Sheriff Court today.

Assistant Chief Constable Tom Wood said that the force had adopted a ''softly-softly'' approach for some considerable time, but there had come a point when they had to clear the road.

''This has nothing to do with the fringe production. At festival time, the police are used to dealing with publicity stunts in a reasonable and liberal fashion. But this event has been hi-jacked by a semi-political protest group.''

The Scottish Ambulance Service confirmed delays had been experienced by drivers making both routine and emergency calls.

A Fringe spokesperson said it understood the main group running the protest was a body which organised demos around the country.

A spokeswoman for ''Road Rage'', none of whose cast was arrested at the protest, said later she was feeling ''a bit shaky'' because of the trouble.

While maintaining the police in general had been fair she said police horses had ''chased'' the marchers up the Mound.

She said the police had wanted to move people on at the Grassmarket because officers felt the protesters had made their point. They also voiced concern that ambulances would not be able to get through to the Royal Infirmary.

She said the members of the Road Rage cast had recently been involved in a tunnelling and earth-shovelling protest in Kent.

''We feel we acted as a catalyst for this event which was in the spirit of the Fringe which produces controversial and topical works.''