The Bank of England has frozen funds linked to a prominent Saudi dissident accused of links to al-Qaeda.
Mr al-Faqih is Saudi Arabia's most prominent exiled dissident
Saad al-Faqih, who heads the Movement for Islamic Reform in Arabia (Mira), is accused by the UN of ties to the terror organisation. He denies the claims.
UK financial institutions have been told not to release Mira's assets.
The Treasury said it had "reasonable grounds" for suspecting the group was acting on behalf of Mr al-Faqih, who lives in exile in London.
A Treasury spokeswoman said: "The Chancellor today instructed the Bank of England, acting as HM Treasury's agent, to direct all UK financial institutions to freeze any funds held for or on behalf of the entity the Movement for Islamic Reform in Arabia immediately."
Series of freezes
"The action has been taken because the Treasury have reasonable grounds for
suspecting that the organisation is acting on behalf of Saad al-Faqih, who was
listed by the UN as an associate of al-Qaeda yesterday."
MOVEMENT FOR ISLAMIC REFORM IN ARABIA
Formed in Saudi Arabia in 1996
Based in London
An offshoot of the Committee for the Defence of Legitimate Rights (CDLR)
Formed by Dr Saad Al-Faqih, a former consultant surgeon
The group seeks freedom of expression and assembly in Saudi Arabia, but has angered authorities
Effectively, it also means any funds belonging to Mr al-Faqih will also be frozen.
The move was authorised under the al-Qaeda and Taleban (United Nations Measures) Order 2001 and is the latest in a series of freezes ordered this year.
The spokeswoman added that banking confidentiality meant the extent of the frozen assets, if any, could not be divulged.
In the early 1990's Saudi political opposition centred on a group partly based in London called the Committee for Defence of Legitimate Rights. Mr Faqih was one of its leading lights.
Using fax machines as its main means of disseminating news, the group released statements critical of the Saudi royal family, alleging corruption and abuse of privileges on the part of princes.
The campaign was effective enough to draw the wrath of the Saudi royal family.
It told the British government that lucrative defence contracts and other commercial deals would be in jeopardy if the group was not silenced.
On Wednesday, the US authorities froze the assets of Mr al-Faqih, who recently called for mass anti-regime protests in the kingdom.
He denied any involvement with al-Qaeda and accused Washington of using anti-terror measures to rescue the Saudi royal family.