The Pakistani, who was among 24 arrested during a series of raids in Lahore and Karachi, was under interrogation last night over the alleged role he played in the terrorist attacks on July 7. “We suspect two or three of the detained [from Lahore] had links with the bombers, but one in particular, who is a major figure in al-Qaeda. We are interrogating them intensively,” one senior Pakistani official told The Times.

The arrests came as a leaked secret report revealed that intelligence chiefs believed three weeks before the London bombings that there were no known terrorist groups with “the current intent and the capability to attack Britain”. The reassurance delivered by the Joint Terrorism Analysis Centre (JTAC), based at MI5, led to the lowering of the alert state from “severe general” to “substantial”.

The leaking of the JTAC conclusion to The New York Times placed the Government and its intelligence advisers in an embarrassing position. Charles Clarke, the Home Secretary, has already said in public that the decision to lower the terrorist threat alert was wrong.

The JTAC report also contradicted the Government’s political stance, repeated vociferously this week, that the events in Iraq had no bearing on the terrorist attacks in Britain. “Events in Iraq are continuing to act as motivation and a focus of a range of terrorist-related activity in the UK,” it said.

Security sources said that the threat analysis was based on the available intelligence at the time. “This was an intelligence gap, not an intelligence failure,” one source said.

It emerged with the first signs of disagreement over whether a foreign mastermind was sent to Britain to orchestrate the attacks, which killed fifty-six people, including the four bombers. Police sources said last night that they believed that a British-born organiser had entered Britain a few weeks before the bombings and left hours before the attacks. They believed that the man, said to be in his early thirties, visited London and the towns where all the four bombers lived before flying out of Heathrow hours before the attacks.

Security sources said, however, that they were still unsure whether an outsider had played such a crucial part in the operation. They acknowledged that initially they had had an individual in mind who they suspected may have come to Britain, and MI5 asked Pakistan to try to trace him.

After a thorough rechecking of all intelligence, however, MI5 had concluded that someone with a similar name had arrived in Britain and then left before the bombings. He was no longer regarded as a suspect.

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