All six Britons held following a Greenpeace protest at an Arctic oil rig have been locked up in Russia for two months without charge.

Four had learned they would be detained for two months last week, with the remaining two, activists Frank Hewetson and Anthony Perrett, remanded in custody on suspicion of piracy following court appearances.

It comes as a group of 30, including the six Britons, were held 10 days ago when armed Russian officials boarded their vessel, the Arctic Sunrise.

The boat and protesters were taken from the Arctic’s Pechora sea, near to oil company Gazprom’s platform, and transferred to the port of Murmansk.

Russian authorities are investigating charges of piracy, which carry a jail term of 10 to 15 years.

Campaigners Philip Ball and Alexandra Harris, freelance videographer Keiron Bryan and engineer Iain Roger learned they would be detained for two months without charge last week.

Mr Hewetson is a long-term activist with the environmental group. His partner Nina Gold described their treatment as “wildly disproportionate and unjust” and said his children were worried for his welfare.

“Frank is an environmental activist trying, on behalf of us all, to defend the Arctic from exploitation by the oil companies through peaceful non violent protest,” she said in a statement released through Greenpeace.

“Two months behind bars without charge is wildly disproportionate and unjust. I would ask the Russian authorities to reconsider this unwarranted and harsh decision. His children and I are very concerned for him but know that he will be cheered by the support of millions of people worldwide which is bringing the destruction of the Arctic to international attention.”