INVESTIGATORS have established a firm link between al-Qaeda and the London bombers after an Islamist terrorist in jail in America identified the British man who led the murderous attacks 10 days ago.
Security officials in the United States have confirmed that self-confessed al-Qaeda member Mohammed Junaid Babar had admitted knowing Mohammed Sidique Khan, the oldest of the British bombers who killed at least 55 people.
Babar, who was arrested after returning from an al-Qaeda "terror summit" in Pakistan early last year, identified Khan from photographs shown to him late last week.
The revelation that an al-Qaeda member was associating with one of the London bombers long before the July 7 bus and Tube blasts reinforces the growing impression that British intelligence failed to spot obvious warning signs of an imminent attack.
Other disturbing security failures are now known to include:
The Leeds-based bombers, far from being quiet and law-abiding, had been banned from three local mosques for as-yet undisclosed unacceptable behaviour;
The failure of a police anti-terror operation to pick up five of 13 suspects, among them, it is claimed, Khan;
A known al-Qaeda operative suspected of masterminding the July 7 attacks visited the United Kingdom two weeks earlier but was not placed under surveillance; and
The Aylesbury-based bomber, Germaine Lindsay, was - according to US officials - on a "watch list" but the British lost track of him.
Babar himself is a Pakistani-American and self-confessed al-Qaeda "sleeper" agent who has already admitted to helping an earlier plot to blow up pubs, train stations and restaurants in Britain.
His links with Khan offer the most significant signal yet that Osama bin Laden's terror network was behind the London attacks, which have now claimed 55 lives.
The global scale of the plot is also becoming clearer. British detectives have arrived in Cairo to question an Egyptian biochemist suspected of being the bombmaker.
Reports in Pakistan yesterday suggested four arrests had been made in the Osman Town neighbourhood of Faisalabad at the request of British investigators.
Now Scotland Yard is poised to send its own detectives to Manhattan to quiz Babar about his claims.
American security expert John McLaughlin, a former acting head of the CIA, said the British investigation had already demonstrated that the al-Qaeda threat was "more widespread than a few isolated guys".
"It will turn out to be a larger network in Pakistan than we might see at this moment, and in the UK," he added. "And it will probably, in the end, turn out to have some linkages into the United States that we'll have to run down."
The reports on Babar appear to corroborate suggestions made last week by French police that there is a link between the July 7 bombings and the attack thwarted by British police in March last year in a co-ordinated raid codenamed Operation Crevice.
Babar, 30, quickly "turned" on his former colleagues once in custody and gave authorities information about a Pakistani terror cell's plot against London discos, bars and restaurants.
During Operation Crevice police seized half a tonne of ammonium nitrate, the explosive material used in devices such as the Bali bomb, and made eight arrests in 24 different locations in England. But French authorities suggested last week that there were 13 suspects in Operation Crevice and five had escaped, possibly among them Khan, a teacher whose driving license was found near the Edware Road blast.
More details have also emerged about Lindsay, the Jamaican-born Briton thought to have carried out the Russell Square underground attack. He worshipped at the same mosque in Brixton as Richard Reid, the shoe bomber, and Zacarias Moussaoui, the "20th hijacker" named by the United States in conjunction with the attacks of September 11, 2001.
Since the discovery of the four suicide bombers last Tuesday police have been struggling to piece together their life story and establish how four men, two of them fathers, were persuaded to join the attack.
The wide-ranging investigation hit an early setback yesterday when Egypt said that it was not prepared to hand over the biochemist detained in connection with the London bombings and that interviews would have to take place on Egyptian soil.
Meanwhile, there is still some doubt whether the four London bombers committed suicide or were duped by their handlers into blowing themselves up in a bid to cover up the plot.
"We've never used the phrase 'suicide bombers'," a Scotland Yard spokesman said. "We've always been aware that amongst the things we need to clarify is the notion these people intended to die as well as letting off a bomb."
Asked what alternative explanations were possible, he said: "Obviously, there's human error of various types or misjudgments of various types. It may seem unlikely, but that's policing - you start with all the possibilities and narrow down the certainties."
Two of the bomber's families yesterday broke their silence over the terror attacks by appealing for help to track down those who masterminded the bombings.
In statements, Lindsay's widow, Samantha Lewthwaite, who is thought to be expecting their second child, said she had no inkling over his plans, while relatives of Kahn said they believed he had been 'brainwashed'.
Lewthwaite, 22, said: "He was a good and loving husband and a brilliant father, who showed absolutely no sign of doing this atrocious crime. We as a family had no idea of his plans and are as horrified as the rest of the world.
"We are still in shock about the news we have been given, and are trying to understand why anyone, never mind Germaine, would do such a thing. We plead to anyone who has information to help police with their investigations to stamp out these terrorists."
The call came after architect Lee Harris, 30, became the latest victim - and the death toll climbed to 55.
Harris, 30, died without knowing sweetheart Samantha Badham had almost certainly been killed in the same attack. The pair boarded the Piccadilly Line tube moments before the bomb went off between King's Cross and Russell Square.
Relatives of 30-year-old bomber Khan, from Beeston, Leeds, expressed their condolences in a statement issued through police.
The teacher, who had a baby daughter and whose wife is also thought to have a second child on the way, was described as "a kind and caring member of our family".
His family said: "We are devastated our son may have been brainwashed into carrying out such an atrocity. We urge people with the tiniest piece of information to come forward in order to expose these terror networks which target and groom our sons to carry out such evils."
Police yesterday moved the twisted wreckage of the double-decker bus where 13 other people died. The bus became a symbol of the capital's worst attack since the Second World War. Londoners and tourists stopped to watch as a flatbed truck with a police escort hauled it away to a secure location for more forensic tests.
Anti-terror officers have also been granted a further extension by magistrates to quiz a man arrested on Tuesday in West Yorkshire.
The 29-year-old was held on suspicion of the commission, instigation or preparation of acts of terrorism. He is currently being questioned at a central London police station.