Two convicted gang killers, transferred out of Cayman’s Northward Prison and sent to a U.K. jail amid alleged “national security” concerns, may have to challenge that decision in London.

Brothers Osbourne Douglas and Justin Ramoon, both serving life sentences for murder, are contesting the decision to transfer them to London’s Belmarsh prison under a 19th-century statute known as the Colonial Prisoners Removal Act.

They were granted leave to apply for judicial review after they filed writs in the Grand Court of the Cayman Islands against the Cayman Islands governor and the director of prisons. They argue that the move breaches human rights, such as the right to a family life, guaranteed by the Cayman Islands Bill of Rights.

Now, government lawyers are seeking to stay the proceedings, suggesting the case should be brought in London.

A three-day hearing in the Grand Court began Monday to assess the merits of that argument and to help determine where the case should be heard.

Government’s lawyers argue that, because the order to move the prisoners was made through powers conferred through an act of the U.K. parliament, the Cayman Islands Bill of Rights is not relevant. They argue that any attempt to contest the decision should be brought in London against the British Foreign Secretary, Boris Johnson, rather than in the Cayman Islands against the governor and director of prisons.

Mr. Ramoon and Mr. Douglas are serving life sentences for the July 2015 murder of Jason Powery outside the Globe Bar in George Town. They were transferred to the U.K. in June 2017. At the time, government said in a statement that the decision was made in the “interests of national security and public safety.”

Both men filed writs arguing that the decision was not justified and breached their human rights.

Representing the two men in Grand Court Tuesday, Hugh Southey QC argued that the Cayman Islands courts would be best placed to handle the substantive issues.

“It would seem very odd for issues, such as whether or not the Cayman Islands can cope with the individuals in question, to be handled in London,” he said.

Mr. Southey said the arguments concerned issues about how the Colonial Prisoners Removal Act relates to the Cayman Islands Bill of Rights, meaning Cayman’s Grand Court was the proper place for the case to be heard.

“What is clear is that the issues raised in the grounds are properly focused on the Bill of Rights. To the extent that there are any real issues in relation to the 1884 Act, they are not independent,” he said. “They require consideration in conjunction with the Bill of Rights, which suggests very strongly these issues should be heard in the Cayman Islands.”