Al Qaeda's British cell planned to attack London's Heathrow airport.

This became clear after British agents arrested 'Bilal,' the man suspected of heading the Al Qaeda cell in Britain earlier this week.

Al Qaeda agents, British agents said, may have used a car or truck bomb in a suicide attack on Heathrow, one of the most frequented airports in the world.  

The British police are now hunting for five Al Qaeda members who eluded arrest during what has been described as one of the biggest counter-terrorism operations mounted in the United Kingdom.

All five men are of Pakistani origin.

The suspected leader of the Al Qaeda cell in Britain, identified by his various aliases -- Abu Musa al-Hindi/Abu Issa al-Hindi/Bilal -- is believed to be a South African national. He was picked up from an address in Willesden, north-west London.

Bilal's identity and location is reported to have come from Mohammad Naeem Noor Khan, the son of a Pakistan International Airlines executive and alleged Al Qaeda intermediary, who was arrested on July 13.

The Times, London, reported that Noor Khan was compelled to stay in touch with his British contacts via e-mail. Once that happened, agents from MI6, the British intelligence agency, tracked down Bilal, even though he is said to have never lived in one location for more than a few days at a time.

Khan, The Times said, provided information about Heathrow -- he was a frequent traveler to Britain, Europe and the US -- to Bilal. The latter and other Al Qaeda members would have executed the actual attack, the newspaper said.

The New York Times meanwhile reported that Bilal, who the newspaper called Abu Musa al-Hindi, was 'by far the most important Qaeda figure detained' after Noor Khan and another key Al Qaeda figure, Ahmed Khalfan Ghailani, were arrested in Pakistan last month.

Ghailani, a Tanzanian, was one of the Federal Bureau of Investigation's most wanted. He was arrested after a gun battle in Pakistan's Gujrat province on July 26.

The newspaper said US officials believed Bilal also helped in the reconnaissance of Al Qaeda targets in the US like the New York Stock Exchange and the World Bank in Washington, DC.

Information recovered from Noor Khan and Khalfan Ghailani led to the highest state of alert in New York, New Jersey and Washington, DC earlier this week.

Eleven other men were arrested in the British raids this week. All the men are said to be of Asian origin; many are British nationals.

The breakthrough came with Khan's arrest, The Guardian reported earlier this week. The newspaper said 'he led US and Pakistani agents to Ghailani and to Ghailani's laptop, on which a plan for an attack in the US had been downloaded.'

Khan, who was educated at Karachi University, passed on encrypted orders from Osama bin Laden and other Al Qaeda leaders to its operatives in America and Britain. He eluded suspicion on his travels, presumably because he did not apparently fit the profile of the standard Islamic extremist. He was personable and spoke with what one British newspaper called 'a flawless English accent.'

Khan and Ghailani's laptops contained extensive information on the construction of buildings like the New York Stock Exchange and the World Bank, 'floor plans of meeting rooms, the configuration of parking garages and even the incline of underground entrances.'

American and British intelligence were shocked to discover the amount of detail -- 'traffic patterns, possible escape routes and details about security guards (their number, shift changes and whether they are armed) as well as discussions about what kind of explosive could do most damage to each of the buildings mentioned,' one newspaper said.