Police are searching a second house in Surrey as part of their investigation into the Parsons Green Tube bombing.
It comes after a second man was arrested in relation to the attack, which left 30 people injured when the device partially exploded on a District Line train on Friday morning.
An 18-year-old suspect was detained at the Port of Dover on Saturday morning and officers later apprehended a 21-year-old man in Hounslow, west London, at 11.50pm.
Police were searching a house in Stanwell, Surrey, on Sunday in connection to the second arrest.
Officers have cordoned off part of the neighbourhood, which lies just outside of Hounslow close to Heathrow Airport.
Police have also carried out a search in Sunbury-on-Thames, Surrey, at the home of foster care couple Penelope and Ronald Jones.
The elderly couple, who received MBEs for their services to children and families, provided a home to the teenager arrested in Dover on Saturday.
They are also connected to a registered resident of the Stanwell property being searched by police, sources told Sky News.
There is no suggestion the couple are involved in the investigation.
