The secrets of 58 Curtis House

Police find bomb-making equipment in north London flat. Suicide bombers returned there after failed attacks. Car used by one of the men found abandoned nearby

Detectives were investigating a witness report that three men returned a day after the 21 July attacks to 58 Curtis House, the north London flat where it is thought the bombings were planned and weapons prepared.

Yesterday, officers discovered chemicals in a nearby lock-up garage, which they suspect may have formed the ingredients for at least five rucksack bombs used in the attacks. They also found traces of the chemicals inside the one-bedroom flat. The discoveries came hours before Metropolitan Police Commissioner Sir Ian Blair revealed there have been 250 incidents since the 7 July attacks when police thought they may have been dealing with a suicide bomber. On seven occasions, police officers have been on the brink of acting: "We have got as close to calling it as 'that' and we haven't," Sir Ian said.

The suspected chemical ingredients found yesterday have raised fears the men may have been able to obtain new explosives before again disappearing, possibly to plan further attacks.

The first real details are emerging of two of the men who had come to Britain as children to escape civil wars in east Africa only to plan bomb attacks in their adopted country which had given them sanctuary. The Home Office said that Muktar Said Ibrahim arrived as a refugee in Britain aged 14 from Eritrea. In November 2003 he applied to become a British citizen and was given a passport last September. He has a criminal record but the details are unclear.

Yasin Hassan Omar, who was 12 when he arrived from his native Somalia in 1992, was brought up in foster care after arriving without family. Enfield Council, which had been responsible for his care, said his benefits stopped last May after the Department for Work and Pensions halted his income support. Omar, who was granted indefinite leave to remain in Britain in 2000, is believed to have drawn £24,000 in housing benefit and £13,000 in income support over the past six years.

His rent of £75 per week was no longer being paid for him and eviction may have followed.

The hunt for the bombers focused last night on the flat in New Southgate, where they had been seen carrying in cardboard boxes which they said contained wallpaper stripper. After a tip-off, police found the flat was used by two of the terrorists. Security sources have denied the property was under surveillance before the raid. When armed police raided the flat in New Southgate early on Monday it was empty.

A neighbour said at least three men were seen in the ninth-floor flat on Friday, including a man matching the description of Omar, whose bomb failed to explode at Warren Street station.

He was the registered tenant at the flat since February 1999 and is thought to have shared the property for the past two years with three other men, including Ibrahim, 27, who tried to blow up the No 26 bus in Shoreditch.

Tania Wright, 32, said she had seen three men in the doorway of 58 Curtis House on Friday. She said: "I came out of the lift and saw three guys in the flat they are now searching. They were nervous. They jumped back inside and slammed the door. When the police made the raid I realised one of them looked like the bomber."

The hunt for the bombers, including a possible fifth attacker who ditched an explosive-laden rucksack, brought more chaos as officers cordoned off a white VW Golf, believed to belong to the men, in East Finchley, two miles east of Curtis House. That led to the A406 being closed.

Ibrahim's family released a statement condemning his actions and saying they had gone to police as soon as they saw a CCTV image of him on the news. The family, from Harrow, north-west London, said: "He is not a close family member. He has not visited for many months."