Greenpeace has swooped on the giant Stena Carron oil-drilling ship off Bressay, clambering up her anchor chains this morning to prevent her leaving to operate west of Shetland.
The surprise raid was mounted after a team of protesters against deepwater drilling quietly left their campaign ship Esperanza in Aberdeen and travelled to Shetland on the NorthLink ferry.
They used speedboats to reach the 228-metre-long Stena Carron's anchorage off the north end of Bressay where she is tended by the oil support ships Esvagt Supporter and Island Champion.
Two activists are hanging in a tent from the anchor chains with their own supplies to keep them going. They were members of the team which carried out a similar action on a rig in the Arctic last month.
Greenpeace said it moved in when there was a sign that the drill ship was about to move after 17 days dominating the north Lerwick skyline.
She is operated by Chevron and is due to start drilling about 125 miles north of Shetland in the Lagavulin field in 500 metres of water near the UK-Faroe median line.
This afternoon the 70-metre Esperanza was south-east of Sumburgh Head, steaming up to join the protest.
The anchorage off Bressay is within Lerwick harbour limits. Lerwick Port Authority chief executive Sandra Laurenson said no action was being taken in relation to the drama.
Greenpeace claims that over 10,000 emails have been sent to UK energy secretary Chris Huhne, calling for a moratorium on deepwater drilling in UK waters following the BP disaster in the Gulf of Mexico.
Greenpeace has also threatened the government with legal action in an effort to stop new licences being granted for deepwater drilling.
The House of Commons energy and climate change committee is currently carrying out an inquiry into the implications for Britain of the Gulf of Mexico disaster, including whether there should be a moratorium on deepwater drilling.
Experts have pointed out that the waters to the west of Shetland are much shallower than those in the Gulf and the UK industry is resisting a halt to drilling work on the grounds that the regulatory regime is much tougher here than in the United States.