Thirty people were arrested today as the environment group Greenpeace began an occupation of an oil rig in a bid to stop drilling in the Atlantic Ocean.
Four protesters climbed on to legs of the Sovereign Explorer in an attempt to prevent it from being towed from the Cromarty Firth near Inverness, where it has been kept over the winter, to drill west of the Hebrides.
The moves followed an occupation of another rig in the same area last weekend by activists who have still not been caught by police after escaping in a motor launch.
Today a spokesman for Northern Constabulary said a total of 30 people were arrested during an operation which began last night.
She said officers were monitoring the protesters from the shore but none were on the rig or planning to approach it.
It is understood the force was tipped off that the protest was due to begin.
The rig was due to begin drilling in the waters west of the Outer Hebrides - the so-called Atlantic Frontier - under a Government licence to explore the area for oil.
The two Greenpeace campaigners who occupied the Jack Bates exploration rig last Sunday had to come down the following afternoon after Sovereign Oil went to court and a judge granted the company an interdict.
But they were not arrested or approached by police after leaving their protest on a motor launch and a report was being prepared for the procurator fiscal.
Today Northern Constabulary said it had no plans to arrest the activists on the rig until they came off and said they had no boat in the area and would wait for them to come ashore.
Greenpeace claims exploration puts the environment west of the Outer Hebrides at risk, threatening its status as Europe's most important habitat for whales and coral reefs.
Rob Gueterbrock, the group's climate and energy campaigns spokesman, said: "All of Britain's conservation groups oppose this drilling yet John Prescott refuses to even comment."
He said the Greenpeace activists intended to continue their occupation of the rig, which is chartered to Marathon Oil, until the Government suspends drilling on the Atlantic frontier.
A spokesman for Marathon Oil said the rig was not yet on contract to the company and was undergoing upgrading work to make it suitable for the deep waters in the Atlantic.
"We have held a licence to drill in this area since 1997. For various reasons we were unable to drill last year and had always planned to drill in the second quarter of this year," he said.
"These activities are entirely within the law and sanctioned by the UK Government.
"Greenpeace is all about soundbites and selective science. The rest of us have to live in the real world."
The rig, owned by TransOcean FedCo For Ex (TSF) was at anchor when it was boarded.
The Marathon spokesman said the two firms were now working together to explore all options and confirmed legal action was one of the possibilities under discussion.
Greenpeace is already facing a £1 million damages claim for its occupation of the Jack Bates platform last week.