A KEY suspect in the alleged plot to mount an attack in Germany on the scale of 9/11 is on the run in Britain, German security officials disclosed yesterday.

Scotland Yard counterterrorism detectives are hunting the man, who escaped from Germany after a plot to explode bombs at Frankfurt airport and a US airbase. The collective power of the bombs would have exceeded those in Madrid and London in 2004 and 2005.

The plot was foiled on September 4 when three men were arrested at a rented holiday apartment near the central German town of Kassel. Police recovered chemicals and bomb-making equipment which investigators believe would have led to the biggest loss of life since the 9/11 attacks in America six years ago.

About 10 other members of the gang were said by German prosecutors to have escaped and one is now in Britain. The arrested three - two of whom were German nationals who had converted to Islam - were alleged by prosecutors to be members of an Al-Qaeda splinter group called the Islamic Jihad Union.

At the time the British and German authorities denied that there were any links between the cell and Britain. Security sources also played down reports that there had been telephone contact between members of the cell and people in Britain.

However, it emerged yesterday that the Germans have told Britain that at least one of the fugitives has since made his way to this country. A security dragnet has been put in place by Scotland Yard’s counter-terrorism command to try to arrest the man.

Wolfgang Schäuble, Germany’s interior minister, revealed last week that the three arrested men had acquired detonators that originated from Syria and had received direct orders to act from operatives in Pakistan. “We know that there is a clear network, highly conspiratorial,” he said after two days of meetings in Washington with US security officials. “The demand came from Pakistan [saying], ‘You should go on for action. Do not go on preparing for months and months and months, but now is the time to take action in the first half of September’ and they did.”

German officials said that the attacks were timed to coincide with the sixth anniversary of the September 11 attacks. The suspects had already assembled the ingredients for homemade bombs: they were caught with 750kg of hydrogen peroxide, a chemical that is easily transformed into explosives.

Al-Qaeda trainers are known to have taught Britons how to use hydrogen peroxide at camps in Pakistan that were attended by other Europeans. The chemical has been deployed at least twice by terrorists in Britain, including the four July 7 suicide bombers who killed 52 people in London in 2005.

The German bombs were designed for an attack on Americans in Germany, possibly at Ramstein airbase and the US consulate in Frankfurt. There were also plans to explode a bomb at Frankfurt airport. Targets were said to include other US bases, a nightclub and a bar used by American servicemen.

The fugitive’s presence in Britain will add to fears that the group may have a network in this country. British and other European intelligence services remain nervous about the possibility of further attacks.

MI5’s Joint Terrorism Analysis Centre, which monitors terrorist threats, says that Britain is still facing a “severe” level of threat - meaning that an attack is “highly likely”.

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