A man has been arrested in connection with the attempted bombings in London on 21 July 2005.
No-one was reported injured in the attempted bombings.
Scotland Yard said the man, 27, was arrested in west London, on suspicion of the commission, preparation or instigation of an act of terrorism.
He is being questioned as police search three premises in west London.
So far 44 people have been arrested, and 16 charged, in the investigation over the failed attacks, which took place on three Tube trains and a bus.
The man, who was taken to Paddington Green station, is not suspected of having been involved in the planning of the attempted attacks.
Police said officers were searching two residential addresses and a business premises in west London.
A Scotland Yard spokeswoman said: "At approximately 11.40am today a 27-year-old man was arrested in connection with the ongoing investigation into the alleged attempted bomb attacks on the London transport network on July 21.
"The man was arrested in the street in Kensington Church Street by officers from the Met's Anti-Terrorist Branch on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000.
"He has been taken to a central London police station where he will be interviewed."
Of those charged over the attempted bombings, five are due to stand trial at the Old Bailey in September for conspiracy to murder.
They are Ibrahim Muktar Said, 27, Ramzi Mohamed, 23, Yassin Omar, 24, Manfo Asiedu, 32, and Hussain Osman, 27.
A sixth man, 23-year-old Adel Yahya, is charged with conspiracy to cause explosions "of a nature likely to endanger life or cause serious injury to property".
The 10 other people face charges of failing to disclose information and assisting the bombing suspects in evading arrest.
The 21 July attacks on the Tube near Warren Street, Oval and Shepherd's Bush stations, and on a bus in Hackney, took place two weeks after four suicide bombers killed 52 passengers on the London transport network.