The hunt for people linked to the London bombings has moved to Aylesbury, 65 kilometres northeast of the British capital.
Forensics experts are searching the market town after police raided a house there last night. No arrests have been made and no explosives found.
Aylesbury lies about 30 kilometres from Luton, from where the four suspected suicide bombers took a train to London.
Meanwhile police have reportedly identified two other suspects.
One is said to be an Egyptian chemistry student at Leeds University who lived in the same area of the northern city as the suspected bombers. He disappeared days before the blasts.
Another is suspected of being the mastermind behind the attacks. He is described as a British-born al-Qaeda operative who arrived in the country by sea three weeks ago and left again hours before the bombings.
Police are still questioning a 29-year old relative of one of the suspected bombers; they have been granted permission to hold the man until Saturday.
He was arrested in Leeds on Tuesday, on suspicion of the “commission, instigation or preparation of acts of terrorism”.