Police said on Friday they were investigating an apparent attempt to set fire to the home of one of the suspected suicide bombers.
Officers went to the home of Jermaine Lindsay in Aylesbury, 65 kilometres west of London, on Thursday evening after reports of a smell of gasoline in the street, Thames Valley Police said.
They confirmed the presence of some kind of fuel. Police have identified Lindsay as the bomber who attacked a subway train between Russell Square and King's Cross on July 7, killing 25
"The substance was found around the family home of the fourth London bomber, which is currently unoccupied," said Superintendent Carole Haveron of Thames Valley Police.
"To conduct a premeditated attack like this is in itself a crime that puts the lives of innocent people in Northern Road at risk," she said.