Forensic teams have cordoned off a home in west London after police arrested a second man over the attack on a tube train in Parsons Green on Friday.
Neighbours described hearing shouting at around midnight from the property in Stanwell at the same time police arrested a 21-year-old in the Hounslow area.
Police have been searching a property in Hounslow since the middle of last night and have maintained a presence at the scene since.
It is not known whether anyone was in the property at the time but Sky News says it is understood to be linked the second arrest as part of the Parsons Green investigation.
At least 30 people were injured when a homemade device failed to detonate properly on a District Line train as it approached the station in west London on Friday morning.
Police arrested an 18-year-old man at the Port of Dover on Saturday morning in connection with the attack.
The man remains in custody at a local police station, but officers are refusing to speculate whether he was attempting to leave the country when he was arrested.
Home Secretary Amber Rudd said yesterday the arrest was ‘very significant’, but added: ‘The operation is ongoing.’
Armed police have also raided a home in Sunbury-on-Thames owned by an elderly couple who have fostered hundreds of children.
Ronald Jones, 89, and his wife Penelope, 71, foster up to seven children at a time and the last eight were refugees, according to Elmbridge CAN, a community group that aims to ‘build a culture of welcome to refugees’.
A former neighbour, who has known the pair for decades, said: ‘They are such a lovely couple – they would do anything for anyone.
‘They were huge figures in the local community, and had such big hearts.’
There is no suggestion the Joneses had any knowledge of any alleged wrongdoing at the property.