The arrest in Pakistan of a key suspect with alleged al-Qaeda links, British national Rashid Rauf, prompted an unidentified associate of his to make the call from Karachi to one of the suspects subsequently arrested in Britain, the officials said.

"This telephone call intercept in Karachi and the arrest of Rashid Rauf helped a lot to foil the terror plan, " a senior Pakistani security official.

It wasn't clear exactly when the call was intercepted, but officials have said Rauf . . . one of at least two Britons of Pakistani descent arrested in Pakistan . . . was held about a week before the plot was foiled in Britain on Thursday.

A British security agency's informer in Pakistan with contacts with Rauf provided a tip that helped Pakistan to arrest him, a Pakistani intelligence official said.

A US official disclosed that, after the first arrests in Pakistan, word went from Pakistan to the London plotters to move ahead quickly, a message intercepted by an intelligence agency. That prompted British police to move in on the conspirators, long under watch.

The plotters allegedly planned to blow up as many as 10 planes flying to the US from Britain. Pakistan says it played an "important role" in breaking the conspiracy in co-operation with British and US agents.

Pakistan's government has confirmed the arrests of seven suspects, and intelligence officials say 10 other people were detained Friday and were being questioned yesterday to determine their links to the alleged plot and where they had received financial support or any training.

An intelligence official confirmed the communication intercept, and said British agents had been monitoring the activities of Rauf 's family since December.

The official said one of the suspects caught in Britain and named by British authorities, Tayib Rauf, is a close relative of Rashid Rauf.

Police believe a fire which destroyed the roof of a mosque may have been in revenge for the alleged terrorist plot.

At about 3.30am yesterday, police and fire crews were called to the Al-Birr Masjid Mosque in Sarum Hill, Basingstoke, after the roof had caught fire.

The blaze took 16 firefighters almost two hours to put out. Nobody was injured. Police said the fire was being treated as arson and an investigation was under way.

Meanwhile, Northern Ireland's most senior police officer wants the Public Prosecution Service to be able to use phone tapping evidence against international terror suspects in court.

Chief Constable Hugh Orde said the provision should be introduced as a weapon of last resort with tight judicial scrutiny but admitted it was not currently viable.

"I do think there are some opportunities, albeit limited, to use evidence or intercepts which you can't currently put before the courts to bring people to justice, " he said.

Sinn Fein West Tyrone Assemblyman Barry McElduff said civil libertarians around the world would attack the practice.