Number 151 Chapter Road in Willesden Green, northwest London, is a double-fronted Victorian house that has seen better days. It is divided into four cramped flats — two up and two down — and its brickwork has been painted a liverish, ruddy brown.

About four months ago, a group of young men took over the tenancy of the right-hand flat on the ground floor. “They all looked of Middle Eastern appearance, and seemed very quiet and studious. I used to collect the rent — in cash — by calling in on the flat once a month,” said Sally O’Sullivan, their landlady.

They appeared to stay at home most of the time. When Ross Dawes, a plumber, called a few weeks ago to fix a drain and replace a hot tap in the kitchen, he was surprised at the number of men he found sitting around on a weekday.

“There were about five men in their twenties and they were all casually dressed in tracksuits,” he said. “They were clearly very religious as they had pictures on the walls and religious artefacts all over the place.”

Last Tuesday, narrow, tree-lined Chapter Road erupted with violent activity as no 151 became the focus of a daylight police raid that may prove to be one of the most significant advances in the war on Islamic terrorism.

As a police helicopter hovered overhead in a stormy sky, armed police in bullet-proof vests burst in and seized the occupants of the flat.

“They smashed in the two front windows,” said a neighbour. “You could see the rock and flagstone used to smash their way in. The lounge was covered in broken glass and looked a complete state.” The landlady was astonished.

A few hundred yards away at the Golden Touch barber and braiding salon on Willesden High Road, another drama was unfolding. Police dragged a man across the floor, according to one account, and dumped him unceremoniously in the back of a van.

Police carried out simultaneous raids in Blackburn and Luton as well as London. In all, 13 men were arrested. Yesterday, 11 were still being held at Paddington Green, the high security police station in west London.

If the suspicions of the officers now questioning the detainees are correct, 151 Chapter Road was a key connection in the network of cheap lodgings around Britain where jihad is discussed and plotted.

More significantly, the delighted American authorities say that one of the men seized in Willesden is probably the top Al-Qaeda operative in this country, a west London Indian who is wanted for a conspiracy to drive truck bombs into buildings housing America’s most high-profile financial institutions. He is known under various aliases, including Eisa al-Hindi (the Indian) and al-Britani (the Briton).

British officials have not confirmed his arrest, and clearly there is room for caution here. To the ill-disguised annoyance of the British police, Washington triggered the wave of anti-terrorist activities on this side of the Atlantic last week. These included the arrest on Thursday of a computer expert at Imperial College, London, whom the United States wants to extradite to face charges that he is a link in the terrorist chain.

If al-Hindi really has been caught, however, it will prove to be the successful culmination of an anti-terror operation by security and intelligence agencies on three continents stretching from Karachi to Manhattan and the scruffy streets of Willesden.

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