Spanish security sources are said to have warned four months ago that Mustafa Setmariam Nasar, a 47-year-old Syrian, had identified Britain as a likely target.

Coded commands from the Syrian, thought to have included threats to other European countries including Britain, were found in a flat raided after the Madrid bombings in March 2004.

Spanish investigators said Nasar, now believed to be in Iraq, had set up a “sleeper” cell of terrorists in Britain. But they believed he was planning an attack to coincide with the British general election in May, rather than the G8 summit last week.

One Spanish website yesterday claimed the General Information Commission, a Spanish police intelligence body, issued a report in March warning that Britain and Spain were the primary western targets. The statement was based on Spanish investigations into the Madrid bombings.

In addition, investigators have noted strong similarities in the methods of the two multiple, coordinated bombings against public transport systems.

Last Friday, a team of Spanish detectives arrived in London to help the Metropolitan police with the investigation.

After last week’s explosions, police were believed to be looking into Mohamed el-Gerbouzi, a Moroccan living in London who has been jailed in Morocco in his absence for terrorism offences. Yesterday, however, senior Met officers were strongly discounting that he had any involvement in the London bombings.

Nasar, from Aleppo, Syria, also known as Abu Musab al-Asuri, who has a $5m (£2.9m) American bounty on his head, is believed to have fled either to Iraq or to the Pakistan-Afghanistan border.

He has connections with London going back more than 10 years, has mixed with many prominent terror suspects and has reportedly been arrested in Britain in connection with bombings on the Paris Metro.

When Nasar moved to London in June 1995 he was already under surveillance by Spanish police, who made a video recording of his departure with his wife Elena. They were accompanied by Abu Dahdah, a Syrian later arrested in Spain, accused of recruiting bombers and now on trial for providing support to the 9/11 conspiracy.

Once in London, Nasar moved his family into a house in Paddock Road, Neasden. From there, he edited the Al Ansar magazine, a newsletter of the Algerian Armed Islamic Group. He became an associate of the cleric Abu Qatada, one of the detainees released from Belmarsh prison last year and accused of being Al-Qaeda’s ambassador to Europe.

In January 1997 he also set up a company called Islamic Conflict Studies Bureau. In documentation filed at Companies House, Nasar describes his nationality as British.

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