From Leeds to London via Luton: the deadly mission of a suicide squad

The station surveillance cameras would later show the four friends chatting away as they strolled down the concourse towards the Underground. "They looked as if they were off on a walking holiday," a senior security source said yesterday.

But the four men were not discussing their holiday; they were about to carry out the first suicide attacks in Britain that would bring terror to London and kill more than 50 people.

The carnage that paralysed the capital last Thursday was not the work of a foreign terror cell, it was revealed yesterday, it was carried out by four friends from Yorkshire.

Earlier that morning the four British men of Pakistani origin had met at Luton train station. Their rucksacks packed with explosives, they boarded the 7.48am Thameslink train and arrived at King's Cross in north London at 8.20am.

As planned the four split at King's Cross tube station, each going their separate ways with their weighty rucksacks.

The friends, three aged 30, 23 and 19, had travelled from Leeds, West Yorkshire, that morning having picked up the mobile bombs, probably from a house in the Burley district of Leeds. The gang is thought to have driven down in two or three hire cars.

The 30-year-old got on to the Circle line train and headed west, travelling four stops to Edgware Road station. At 8.50am - the agreed time for the attack, just as the train was pulling out of the station he detonated the bomb. Seven people died in the blast and more than 100 were wounded, at least 10 seriously.

At the same time the 23-year-old - believed to be Shahzad Tanweer - who had travelled in the opposite direction on the Circle line, was between Liverpool Street and Aldgate when he set off the high-explosive bomb, killing at least seven people.

The third synchronised explosion was to be the most deadly. The suicide bomber travelled south on the Piccadilly line and had travelled several seconds out of King's Cross station on his way to Russell Square when he detonated his device. This explosion - in the narrow confines of a deep-lying tunnel - caused the greatest injuries with more than 21 killed. The terrorist is thought to be among the dead, although the police have yet to identify him among the mass of body parts to be recovered from the scene.

The youngest of the group, Hasib Hussain, 19 is thought to have planned to head north, but the Northern line was closed so he headed to the street above King's Cross and caught a No 30 double-decker bus. It was nearly an hour later, at 9.47am that he set off his bomb in Tavistock Square, killing at least 13 people.

The first the police became aware of any of the killers was when Hussain's parents contacted the Scotland Yard emergency helpline at about 10pm on Thursday to report that their son had been travelling to London with three friends and had not been heard of since.

The parents were allocated a police family liaison team amid fears that their son was a victim of the terrorists.

Two of the terrorists were from Leeds, the other two came from Dewsbury, West Yorkshire.

The police began to suspect that they may be dealing with a suicide bomber because the bus bomb had been an hour after the others - which at the time were thought most likely to be on timers. They were all set off within 50 seconds of one another.

But the breakthrough came at about 8pm on Monday night when the police, trawling through hundreds of hours of video recovered from 2,500 surveillance cameras, found a picture of the 19-year-old at King's Cross, with three other men all carrying large ex-Army-style rucksacks.

The police traced each of the suspects via documents they left at the crime scenes, including credit cards. They were later able to find the body parts of three of the terrorists, but the man travelling on the Piccadilly Line has still not been identified.

With the discovery Scotland Yard's anti-terrorist branch organised early morning raids, hoping to catch other gang members and to recover explosives.

At 7.05am yesterday, police raided an address at Thornton Park Avenue, in Dewsbury, West Yorkshire, where retired and recently widowed former high school teacher Farida Patel lives.

Within an hour or so, police raided an address at Lees Holm, council houses a five-minute drive away, where Mrs Patel's daughter Hasina, 23, has been living since January with her husband Rashid Facha - in his late 20s and of Pakistani extraction - and their eight-month-old daughter. Police arrived at the house at 8.15am and Mrs Facha was led away in her veil. A neighbour said Mr Facha had been missing since last Thursday.

In Beeston, 10 miles away, two hire car workers arrived soon after 9am in search of a Nissan Micra car which had been hired from the First 24 Hour company in the city's Headingley district the Friday before last. It hadn't been returned. They found the street they needed - Colwyn Road - taped off by police, who had been there since 6.30am, and were questioned about the car.

Neighbours said a resident of the house under investigation - Shazad Tanweer, 23, had also been missing - since last Friday. His father did not appear yesterday at the fish and chip shop he runs. His son was said by friends to have been university educated and a keen cricketer.

Special branch officers and police also taped off the road in front of a house in Stratford Street in Beeston. The occasional residents here in recent years have been Naveed Fiaz, in his mid-20s, who still lives in the district with his English wife, Tracey, and their three children and his brother Eliaz (known as 'Jacksy').

Brought up in the house for 15 years by Mohammed Fiaz and Hamida Begum, both men have only been seen there occasionally in recent years. Eliaz, 30, visited every two months or so.

Another house raided was in Colonso Mount, in the Holbeck area, where Hasib Hussain, 19, and his older brother were raised by their parents Mahmood and Maniza. Hussain has had a troubled adolescence. Locals said his parents tried to discipline him but he became devoutly religious about 18 months ago. He is believed to have gone to London last week and has not been seen since.

Police searched the houses for "explosives and other bits and pieces" according to one senior officer. At the house on Thornton Park Avenue, a silver Ford Escort and a Honda were removed.

The most dramatic events of the day unfolded in the Hyde Park Road area of Burley, where a convoy of police vehicles arrived at around 11.30am and 500 houses were evacuated as police carried out a series of controlled explosions. Police discovered what a senior source said was a bomb factory, that included high explosives thought to have been used in the suicide attacks.

There was worry for individuals locals believed were living ordinary lives. Azzy Mohammed, 21, a friend of Tanweer, said: "He's one the best lads I've ever met. He was just a guy I liked to play cricket with."

At 5pm, the Deputy Assistant Commissioner Peter Clarke, head of the Anti-Terrorist Branch, told a press conference that Britain had been the victim of suicide bombers for the first time.