Anti-terrorist officers believe that a man arrested in Birmingham today is one of the would-be suicide bombers who attacked the London transport network last week.
As police investigations into last week's bungled bombings spread across the country, another man was detained under anti-terror legislation at Luton airport as he was about to catch a Ryanair flight to the southern French city of Nimes. It was not clear whether there was any connection with the London attacks.
But the Birmingham arrest appeared to be a significant breakthrough for police. A witness said that the man arrested in Heybarnes Road, Hay Mills, looked like Yasin Hassan Omar, 24, who has been named by Scotland Yard as the man who tried to explode a bomb on the Victoria Line Tube line last week.
The man was felled with a Taser stun gun after a scuffle with police officers who raided a house at 4.30am. The BBC reported that the man had been wearing a rucksack as he was arrested, although Scotland Yard could not confirm that report.
Police found a suspect package and more than 100 nearby homes were then evacuated on Army advice as the bomb squad moved in.
The suspect was taken to Paddington Green high security police station in Central London for questioning. Shortly after his arrest, three other men were held in a raid two miles away in Bankdale Road in the Washwood Heath area of Birmingham and are being held by local police.
The raids were carried out by 50 officers from the Metropolitan Police Anti-Terrorist Branch and West Midlands Police. No shots were fired.
Two other men travelling on a train from Newcastle to King's Cross were arrested last night after the train was stopped at Grantham in Lincolnshire. Police said that the arrests, under the Terrorism Act 2000, followed a tip-off from two off-duty Metropolitan Police officers on the train.
Andy Wilkinson, an electrician who lives in Heybarnes Road, Birmingham, said that he saw the suspect being led out in a white forensic suit with his hands bound by plastic ties. He said the suspect looked like Omar but could not confirm that it was him.
Mr Wilkinson, 41, said: "It was about 5.10am and all we could hear was a right racket - people trying to break a door down. I looked out of the window and the road was full of armed police and they had got the road closed off.
"After 10 or 15 minutes they brought a guy out. He looked like the darkest-skinned one in the photos of the four suspects released by the police - the one with the curly hair.
"They had him dressed in one of those white suits. He had plastic cuffs on the front and just after he came out, they brought a woman out and she looked Filipino."
Mr Wilkinson said the maisonette property that was raided had been rented for a long time. He said: "According to the old bloke who lives next door, they come and go and they are not there all the time. It's almost like it's a letter drop. You don't see them for three days at a time."
Bedfordshire Police said that a man was detained at Luton airport as he prepared to take a flight to Nimes. The flight was delayed for several hours while police checked the aircraft and sparked a major security alert at the airport.
Deputy Chief Constable Martin Stuart said: "I would like to reassure everybody that their safety is our priority and apologise for the delay to this flight, but it is important that all calls to the police are thoroughly investigated. Again, we apologise for the inconvenience this has caused."
Today's arrests in Birmingham are thought to be of major significance in the hunt for the bombers. Detectives fear they may still be in possession of explosives after reports that on the day after the failed July 21 attacks they returned to the tower block flat rented by Omar that they had used as a bomb factory in New Southgate, North London.
A resident there claimed she saw three men outside the ninth-floor flat on July 22. Tanya Wright said: "As I was walking towards the stairwell, there were three men stood outside the flat. They looked very suspicious, very worried. They panicked and jumped back into the flat and slammed the front door."
It is also understood that police have recovered a large amount of chemical compounds from a lock-up near the tower block which could have been used to make home-made explosives. Two other North London premises, in Finchley and Enfield, were raided by Scotland Yard's anti-terrorist branch this morning, although no arrests were made.
Omar and another man Muktar Said-Ibrahim, 27, have been named as suspects over the July 21 attacks. It has emerged that Ibrahim was jailed at the age of 17 after being convicted for a number of violent muggings. He had arrived as a refugee with other asylum seekers from Eritrea in East Africa when he was 14. In November 2003 he applied to become a British citizen and he was given his British passport last September.
The Home Office was unable to comment on how he was able to obtain a British passport following his reported conviction and prison sentence.
Omar has also been in the UK for more than 10 years. He arrived from his native Somalia at the age of 12 and in May 2000 was granted indefinite leave to remain. Scotland Yard refused to confirm whether Omar or Ibrahim were arrested this morning.
Residents in Barkdale Road said that three young Somali men in their 20s had lived in the semi-detached house for about six months - although neighbours had no contact with them.
Joseph Tilt, 49, a neighbour of the raided property, claimed that he heard gunshots after being alerted to the police presence. He suggested that several volleys of shots were fired as police shouted for the residents of the house to open the door.
The father of six, who works as a children's carer, added: "We were in bed and we heard these big bangs. We looked out of the window and there was a flash and others started shouting.
"There were armed police along the road and the roads were already cordoned off. And they were shouting 'Open the door'."
Mr Tilt said he saw two of the three people being taken away in unmarked cars. He added: "I thought at first it must be something to do with drugs or something of that sort because that happens a lot around here."
Mr Tilt, and his near neighbour Angela Bolton, both described the people at the property as "Somalians" but said they did not have any contact with them. Three people - two men and a woman - lived in the property, Mr Tilt said, and had been living there for about five to six months.
Roger Godsiff, the Labour MP who represents Birmingham Sparkbrook and Small Heath, said that he hoped today's arrests would not strain community relations.
"I hope wise counsels will prevail. It's an old 1930s council estate - primarily houses, very few flats. Many of them were bought by sitting tenants, a complete mixture - white families, Afro-Caribbean, long-established Irish community, Pakistanis, Kashmiris, Bengalis, Indians, Sikhs, Somalis," he said.
"Community relations in the area have always been very good and I hope very much indeed that anybody who seeks to exploit what has happened for their own personal or political gain will be very much put down by the community.
"I hope very much the community will work together to try and ensure that the good community relations continue."
He added: "The Muslim community have to stand up. They have to confront those people within their community who they know are contorting what the Koran stands for and are also seeking to spread information which quite frankly has got no reality whatsoever to the facts of life."
Ibrahim is thought to have turned to radical Islam while serving a five-year sentence for being part of a gang that carried out a series of muggings at knifepoint at Hertfordshire railway stations.
He qualified for early release in 1998 and is then alleged to have met Richard Reid, the jailed "shoe bomber", at two London mosques. Reid, who was also a petty criminal, tried to blow up an airliner over the Atlantic in 2001.
Passport checks have been re-imposed for everyone leaving the country in an attempt to prevent the four suspects from fleeing abroad. Controls were imposed after the first wave of bombings on July 7 and were back in place only four days after being lifted.
Armed police have also seized a car used by one of the bombers, which was found abandoned a few miles from the council flat that Ibrahim and Omar shared. Streets near the North Circular Road in East Finchley were sealed off as bomb disposal teams searched the white Volkswagen Golf.
Police told how Ibrahim was identified by his own parents. His family spoke of their shock at discovering their son's involvement in terrorism and condemned his actions. "We are a peaceful family, having lived in this country since 1990," a family statement said.
Police are still checking identifications of the other two men who took part in the attacks.
Sir Ian Blair, the Metropolitan Police Commissioner, said that senior officers had come close to allowing officers to fire on terrorist suspects seven times since the July 7 bombings. They had been asked to assess the risk of a terrorist 250 times in the past 20 days.
The body of the Brazilian man shot dead by police will be flown back to his home country tonight. Jean Charles de Menezes, 27, was gunned down at Stockwell Station on the
London Underground on Friday.
Plain-clothed police officers shot the electrician eight times.
Today, solicitors for Mr de Menezes said his body was being returned to Brazil for a family funeral. Relatives of the dead man will travel on the same flight.