Shocking new images have emerged of unexploded bombs, some packed around with nails, which were found in a car left behind by the July 7 London bombers.
In total, 16 bombs were found in the red Nissan car parked at Luton railway station. It is is believed the car was rented in Leeds by Shehzad Tanweer, one of the four bombers who killed themselves and 52 others in a co-ordinated attack on three London Underground trains and a bus earlier this month.
The sheer number of devices has raised fears that the scale of the July 7 bomb plot was much larger than originally imagined.
The presence of nailbombs graphically illustrates that the bombing cell wanted to inflict the maximum possible pain, injury and risk of death on innocent London commuters, security analysts say.
"You see what is bulging on the sides of the bottle are nails. Many, many nails," said Robert Ayers, a security expert who was shown the pictures by the American ABC News channel last night.
"And the nails are put there so that when the bomb goes off, the nails will tear tissue and kill people in the area. Bombs don't kill by concussion. Small bombs, they kill by the blast effects of fragments of glass or metal, and this is designed to kill people."
Meanwhile police were continuing to question Yasin Hassan Omar, named by police as one of the would-be terrorists in the attempted second wave of London bombs on July 21. Omar is believed to have been on the run since a bomb failed to detonate on a tube train at Warren St station last Thursday. Three others, whose devices also failed to go off, are also wanted by police.
Omar was felled with a Taser stun gun after a scuffle with police officers who raided a house at 04.30.
Police found a suspect package and more than 100 nearby homes were then evacuated on Army advice as the bomb squad moved in. He 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.
Meanwhile today Luton airport was closed and flights thrown into disarray as a man was arrested under the Prevention of Terrorism Act as he was about to catch a Ryanair flight to the southern French city of Nimes. It was not clear if this was in connection with the bombings.
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.
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.
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 shot eight times in the head at Stockwell Station on the London Underground on Friday.
Today his family said in a press conference that the electrician had acted as "training" for the security forces. They said that by shooting dead 27-year-old Jean Charles de Menezes the police had learned the wrong course of action - and were now using stun guns instead.
Alex Pereira, 27, said his cousin's death had given police a lesson they needed. "They learned, it means that my cousin was training. They killed one person to learn that lesson, I hope they never kill again."
He added: "They would never have learned this if my cousin had not died."