British counterterror police arrested two further suspects, a 48-year-old man and a 30-year-old man, in the Welsh city of Newport on Wednesday.
Yayyah Farroukh was seen outside the Aladdins Fried Chicken shop in Hounslow, West London, being pinned down by police at midnight on Saturday. The 21-year-old defendant is now being held under the Terrorism Act.
The terror alert in Britain was raised to its maximum "critical" level on Friday, meaning another attack was believed to be imminent.
"Searches are continuing at two addresses in Surrey and a commercial property in Hounslow in connection with this ongoing investigation".
The second man to be arrested by police with regards to the Parsons Green terror attack has been named as Yahyah Farroukh.
Images of the bomb posted on social media appear to show a bucket on fire that had been placed inside a plastic bag close to a rail auto door.
A map showing the location of major developments in the Parsons Green bombing investigation. Google Maps Business Insider
A Metropolitan Police statement did not say how the men might be linked to the bombing.
Previous attacks in London this year at Westminster Bridge, London Bridge and Finsbury Park as well as a blast at an Ariana Grande concert in Manchester killed dozens of people and injured more than 150.
Footage has emerged of a man in Sunbury carrying a Lidl bag, similar to the one the suspected device was hidden in, at 6.50am, reportedly leaving a house which police later searched.
The home-made bomb shot flames through a packed train carriage at west London's Parsons Green Tube station during the Friday morning rush hour but apparently failed to detonate fully. The family had been honored by Queen Elizabeth II for their fostering services in 2010, awarded with Member of the Order of the British Empire (MBEs) "for services to children and families".
The so-called "Islamic State" has claimed responsibility, but authorities have not found evidence that the attack was ordered or organized by the militant group. This property was raided by police on Sunday and continues to be examined by police.
"There is increased police activity in the area but no local evacuation will take place".
Four other violent attacks in Britain this year have killed 36 people.
Mr Rowley said that, although the reduced threat level meant that the role of armed soldiers in policing duties would be phased out over the next week, armed police would continue to patrol the streets and the transport network.