The London terror bombings were the first suicide attacks on British soil and were carried out by home-grown terrorists, police sources revealed tonight.
Police said they believed four men who arrived at King's Cross last Thursday morning on a train from Leeds were behind the terrorist bomb attack that killed at least 52 people on three tube trains and one bus.
At least three of the bombers are believed to have been British males of Pakistani origin who lived in West Yorkshire. Detectives are still unsure about the identity of the fourth bomber.
The bus bomber is believed to be dead, and police said there was "strong forensic and other evidence" a second bomber died at Aldgate. Investigators are now trying to establish if the other two are alive or died in the explosions.
A relative of one of the suspects was arrested in West Yorkshire today and was being brought to London to be quizzed by the anti-terrorist branch.
Police sources tonight said that they were working under the assumption that the attacks were carried out by suicide bombers.
Suggestions that the bus was targeted by a suicide bomber were initially denied by police, but witnesses claimed an "agitated" passenger was seen rummaging in his bag.
Deputy assistant commissioner Peter Clarke, the head of the Metropolitan police's anti-terrorism branch, said CCTV footage at King's Cross station showed the four suspected bombers together at 8.30am.
The three tube blasts - at Aldgate, King's Cross and Edgware Road - came within a minute of each other at 8.51am. The bus bomb detonated 57 minutes later as the No 30 passed through Tavistock Square in Bloomsbury, central London.
DAC Clarke said police were now trying to establish the movements of the four men in the week before the bomb attacks.
"We are trying to establish their movements in the run-up to last week's attack and specifically to establish whether they all died in the explosions," he told a press conference tonight.
Six search warrants were today served under the Terrorism Act on houses in and around Leeds, during the operation in which one man was arrested.
"These included the home addresses of three of the four men," DAC Clarke told reporters. "A detailed forensic examination will now follow and this is likely to take time to complete."
The investigation has already established that personal documents bearing the names of three of the four men were found close to three of the explosions.
Property in the name of the suspected bus bomber - reported missing by his family on the morning of July 7 - was found on the No 30.
Property of a second man was found at Aldgate, and property belonging to a third was found both at Aldgate and at Edgware Road.
In a further development, police have found explosives inside a car left outside Luton railway station in Bedfordshire.
A controlled explosion was carried out on the vehicle, which was expected to be removed for forensic examination. Officers could not say how long the car had been parked there.
Metropolitan Police bomb squad officers have since removed the explosives. A spokesman for Bedfordshire Police said: "They think they have found some explosives and they have taken them out of the car and that is what they are going to explode safely."
The operation began today at 6.30am with searches on the West Yorkshire addresses, the first raids in Britain in connection with the attack.
Armed officers and army bomb disposal experts took part in the raids on the properties in the Leeds area. Materials seized during the operation and have been taken away for further examination.
At least one controlled explosion was carried out ahead of a raid on one of the properties, where police on the ground said they were searching for explosives.
Around 500 to 600 people were evacuated from the area close to the address in the Burley district of Leeds at around 11.30am. Army officers used a controlled explosion to gain access to the property at 1.20pm.
Neighbours said a 22-year-old man had lived at the house on Hyde Park Road with his family but had gone missing.
The operation in Leeds was being led by the Metropolitan police anti-terrorist officers with the support of West Yorkshire police and the army bomb disposal unit. Armed officers had been used as a precaution in case anyone was inside the property.
A house in Lees Holm, Dewsbury, West Yorkshire, was one of those surrounded by police. Scaffolders arrived in the afternoon and began erecting a platform at the rear of the property.
Police officers guarded the front of the terrace house and a police van blocked off the road, preventing people from visiting the scene.
Forensic investigators could be seen entering the house wearing masks and protective suits. Neighbours on the council estate said an Asian couple lived there with a young baby daughter. It is believed that the baby was aged about eight or nine months, a resident said.
Neighbour Sara Aziz, 28, a mother of two children, said the couple had not been there for more than a year. She said the man was aged about 29, while his wife was several years younger. She said the couple originally came from Pakistan but had moved from Leeds.
She added: "She left with the police this morning wearing a veil. He wasn't there this morning. I last saw him last week."
Earlier police cordoned off a white semi-detached house in Colwyn Road, a quiet residential street in the Beeston area of the city, and a terrace house in Stratford Street, around two minutes' walk from Colwyn Road. Material was seized during the raids and has been taken away for further examination.
· The Muslim Council of Britain is considering holding a national demonstration of protest against the terrorists behind the London bombings. The inter-faith event, which has yet to be agreed, would involve marches in the capital and other cities across the UK.
