No serious incidents were reported, but the protests heightened fears of confrontation on the streets when leaders of the world's top industrialised nations convene at the secluded Gleneagles golf resort from Wednesday.

Police arrested four people at Faslane naval base, where more than 700 mainly young protesters -- dancing, beating drums, or lying on the pavement -- blocked the gates in and out of the facility.

In Edinburgh, at least three clusters of anti-G8 protesters, each about 250 strong, were seen by an AFP reporter in and around the city's financial district, home to some major British investment and insurance firms.

Police drew batons and scuffled with a small number of demonstrators, while one group of about 60 troublemakers were seen being coralled into a side-street to head off acts of violence.

Riot police were on alert for the unauthorised "Carnival of Full Enjoyment", which took place two days after more than 200,000 marched peacefully in Edinburgh to demand robust G8 initiatives to counter poverty in Africa.

More than 10,000 police, many imported from other parts of Britain, are deployed at Gleneagles and elsewhere in Scotland this week in the biggest security operation ever mounted in Britain for an international summit.

"This protest is about anti-militarism and the G8," spokeswoman Ruth Tanner of the Campaign for Nuclear Disarmament told AFP at the main North Gate of Faslane, home of the Royal Navy's Trident-toting strategic submarines.

"Ninety percent of arms dealing comes out of G8 countries. You can't make promises about poverty when you're pumping so much into arms," Tanner said, alluding to Prime Minister Tony Blair's desire to see the Gleneagles summit produce an agreement on African aid, trade and debt.

A Ministry of Defence spokesman called the protest, under partly sunny skies, "much more low key than we expected".

"The reason I'm doing this is to raise awareness about the scandalous spending on Trident nuclear weapons," said Johnny Barton, 33, who spent all day sitting uncomfortably atop Faslane's 10-foot (three-metre) perimeter fence.

He was arrested upon descending for breaching the peace, but soon released -- much to the cheers of his fellow demonstrators.

Three other people were arrested for jumping over the fence into the less-secure oil depot area -- a 24-year-old male and two young women who told AFP they were from Sweden.

This week's summit of G8 countries -- Britain, Canada, France, Germany, Italy, Japan, Russia and the United States -- is to discuss joint steps to combat extreme poverty in Africa as well as ways to deal with climate change.

Four Vanguard-class nuclear submarines which carry Trident missiles are based at Faslane, on the Clyde estuary. Some 9,000 Royal Navy personnel, civilian defense workers and subcontractors work there.

Literally hundreds have been arrested at previous Faslane protests for attaching themselves to the gates of the base in acts of "direct action" and civil disobedience.