AT Scotland Yard we were amazed and dismayed when, in April, a jury at the Old Bailey cleared eight of the men charged with involvement in the ricin plot.

My warnings about terrorist activity in the United Kingdom were amply justified by the ricin affair. This came to public notice only this year, but by then officers of our anti-terrorist branch had been working on the case for more than two years. A major part of the inquiry had been the raid on Finsbury Park Mosque in north London.

Investigations began in September 2002 when intelligence contacts warned us that a network of Algerians in this country were raising funds for terrorism. They were buying goods with stolen or forged credit cards, and selling them back. Most of the money was finding its way into terrorist hands.

In England our people identified three or four separate groups — about eighty people in all — working in different parts of the country, but when we launched Operation Springbourne, we concentrated on one group in London, raiding all their addresses simultaneously and arresting 15 of them.

Of the 15 suspects one managed to leave the country, but we traced him to Algeria and re-arrested him there. It was he who told the authorities that people had been manufacturing ricin poison in London and this led us to the flat in Wood Green, north London, which we raided on January 5, 2003. In the scruffy apartment we found ingredients for the poison along with other recipes. Our intelligence — though we could not prove it — was that the occupants of the flat were planning to mix ricin into jars of face-cream and smear it on the doors of Tube trains and restaurants in the hope of causing deaths and spreading panic. Two jars of cream remain unaccounted for.

Until then we had not heard of a man called Kamel Bourgass, also known as Nadir Habra. Now it emerged that he had entered Britain illegally in 2000, had been refused asylum and later disappeared.

After his fingerprints had been identified in the flat at Wood Green all Special branches were alerted with a warning that he was dangerous; but it was pure chance that on January 14 he was accidentally cornered in a flat in Manchester during a hunt for another suspect. He tried to escape, stabbing Detective Constable Stephen Oake to death with a kitchen knife.

The poison recipes led directly to the raid on the Finsbury Park mosque later in January, and it was a moment of carelessness by one of the terrorists that gave them away. In Wood Green documents were found in a re-used envelope on which someone had obliterated an earlier address by inking over it. Forensic examination revealed that under the top layer of writing was the address of the mosque.

Operation Mermant, the raid on the mosque, carried very high risks and was authorised by Assistant Commissioner David Veness for the night of January 19, 2003.

Every precaution was taken to avoid hurting Muslim sensibilities. Beforehand, we arranged for anyone coming to prayer early in the morning to be diverted to another mosque nearby. All police officers who were to enter the mosque wore overshoes and headgear, and the raiding party included Muslim officers to handle copies of the Koran.

Elaborate assessment of the risks was carried out, for we knew that there were terrorists inside, and that they had weapons. The most drastic possibility was that they might have set explosives around the building so that they could blow it up at a moment's notice. More probable was that one of them might blow himself up if he found himself under attack. Speed and surprise were therefore prerequisites.

Around 2am more than 1,000 officers were briefed at Scotland Yard, ferried up to the site in a convoy of cars, vans, trucks and buses, and deployed round the mosque, sealing it off in a complete ring. Firearms officers were on stand-by.

When everyone was in position, Detective Superintendent Colette Paul — leading the raid on her birthday — gave the signal by radio. All ground-floor doors and windows were smashed simultaneously, and she was first in through the main door. In the fetid basement eleven men were asleep on the floor, lying on scraps of carpet — not even on mattresses. Some were taken by surprise so completely that they were handcuffed where they lay. Others jumped up and tried to run but were brought down in the hall. All were arrested, including the two most wanted men, and taken straight to various police stations.

The search revealed that although the main prayer rooms were obviously a genuine religious centre, the office, basement, kitchen had been used for terrorist activities.

When news of the operation became public, many people were sceptical, and questioned whether such a violent assault had been necessary. In fact the information gained from it sparked off a huge investigation into terrorist activities, extending to twenty-six countries.

The jury’s verdict was very disappointing — but questioning such decisions, other than to learn lessons from them, is not productive. Such setbacks are something that every police officer has to learn to live with.

Extracted from Not for the Faint-Hearted: My Life Fighting Crime by John Stevens, Metropolitan Police Commissioner 2000-2005, to be published by Weidenfeld & Nicolson, September 19 at £18.99. © Lord Stevens of Kirkwhelpington 2005. Copies can be ordered for £17.09 with free delivery from The Times Books Direct on 0870 165 8585

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