Police are continuing to question two men on suspicion of terror offences following Friday’s attack on a Tube train in south-west London.
It comes as CCTV images emerged showing a man carrying a Lidl supermarket bag 90 minutes before the bombing.
An 18-year-old and 21-year-old are being held over the explosion, which injured 30 at Parsons Green station.
The UK terror threat level has been lowered to severe after being raised to critical, its highest level.
On Saturday, the 21-year-old, believed to be Yahyah Farroukh, was arrested in Hounslow, west London, and the 18-year-old was detained at Dover port.
Local council leader Ian Harvey said he understood the 18-year-old was an Iraqi orphan who moved to the UK when he was 15 after his parents died.
Police are searching two addresses in Surrey in connection with the arrests – one in Sunbury-on-Thames and another in Stanwell, near Heathrow airport.
Mr Harvey, who leads Spelthorne Borough Council, told the Press Association it was “widely known” the 21-year-old was a former foster child who had lived at the property being searched in his ward of Sunbury East.
A third property in Hounslow has also been searched as part of the investigation, Scotland Yard said.
The BBC understands it is a Middle Eastern chicken shop called Aladdins in Kingsley Road.
ITV News has obtained CCTV showing a person leaving the property in Sunbury that is currently being searched by police.
The person can be seen carrying a Lidl bag at 6.50am on Friday morning.
At 8.20am, a device exploded on a District Line train.
The “severe” terror threat level means an attack is no longer imminent but is still highly likely.
Home Secretary Amber Rudd said police had made “good progress” in the investigation and urged “everybody to continue to be vigilant but not alarmed”.
Assistant Metropolitan Police Commissioner Mark Rowley said police had gained a “greater understanding” of how the bomb was prepared but said there was “still much more to do”.
Source: BBC News