The statement, under the name of the Secret Organisation of the al-Qaida Jihad in Europe, said: "The heroic mujahideen have carried out a blessed raid in London. Britain is now burning with fear, terror and panic in its northern, southern, eastern and western quarters."

It was posted on an Arabic website, al-qal3ah.com, which is registered by Qalaah Qalaah in Abu Dhabi and hosted by a server in Houston, Texas. But two Israeli groups devoted to exposing the network of jihadist sites claim that it is connected to the London-based Saudi dissident Saad al-Faqih. Mr Faqih, who is based in Willesden, north-west London, and runs the Movement for Islamic Reform in Arabia (Mira), was designated by the US treasury last December as a supporter of al-Qaida. The UK Treasury followed suit by freezing Mr Faqih’s assets.

Speaking in December 2004 before the assets were frozen, Mr Faqih ridiculed any idea that "millions of dollars" would be frozen. "I have no assets in the US and all I have in the UK is a current account with a few hundred pounds."

The US claimed that Mr Faqih was an associate of Khaled al-Fawwaz, who was arrested in Britain on a US extradition warrant for his alleged involvement in the 1998 east African embassy bombings.

The US said that "extremists utilise a website controlled by al-Faqih and Mira on messageboards to post al-Qaida-related statements and images. While Mira has issued disclaimers warning users to not attribute postings on Mira message boards to al-Qaida, information available to the US and UK governments shows that the messages are intended to provide ideological and financial support to al-Qaida affiliated networks and potential recruits."

Mr Faqih has always vigorously denied being involved with terrorism. Yesterday he was indignant about being linked to the website.

"It does not belong to me at all," he told the Guardian. "It is a Zionist smear."

He had seen the message on Thursday morning and doubted its authenticity. "It was only there for a few minutes, and they misquoted the Qur’an." He also said the website - or more accurately a bulletin board - could be used by anyone.

The server in Houston has intriguing connections. Everyone’s Internet was founded by brothers Robert and Roy Marsh in 1998 and by 2002 had an income of more than $30m (now about £17m).

Renowned for his charitable work, Roy Marsh counts among his friends President George Bush’s former sister-in-law, Sharon Bush, and the president’s navy secretary.

Everyone’s Internet, which also hosts a number of pornographic sites, states: "We support the uncensored flow of information and ideas over the internet and do not actively monitor subscriber activity under normal circumstances."

However, the company has responded to requests to take down objectionable material and insists it cooperates with US law enforcement agencies.