The Foreign and Commonwealth Office (FCO) says it believes the five sailors are being held on the island of Sirri.

BBC: Iran issues warning over UK yacht crew

The arrest in London of Yasser al-Sirri, a leader of Egypt's Gamaat Islamiya, was greeted in Cairo with particular glee.

ECONOMIST: Arab dissent

Yasser al-Sirri, an Egyptian-born Islamist who has resisted efforts to extradite him to America, made a detailed appeal, based on sharia law, for Mr Bigley's freedom.

ECONOMIST: British Muslims try to unite over a hostage crisis

But as Erik Sirri, a senior official at the Securities and Exchange Commission pointed out in a speech on November 28th, other forces were at work too.

ECONOMIST: Risk management

"They're quite receptive, " says Sirri.

FORBES: Arab Anger, Inc.