Shortly after the bombing, the United Kingdom raised the terror threat level to "critical" in response, but lowered it back to its second highest level on Sunday, meaning an attack was highly likely but not imminent.
The fact that a second person a 21-year-old man was arrested under the Terrorism Act offered the clearest proof yet that police and security services believe the subway bombing was not just the work of one person.
"It is inevitable that so-called Islamic State or Daesh will try to claim responsibility, but we have no evidence to suggest that yet", she told the BBC.
"We will continue to assist with the investigation in any way we can".
Another man was arrested late Tuesday night in Newport, where police raided several homes. There are now two searches continuing at addresses in Surrey and we are getting a greater understanding of the preparation of the device.
"A significant amount of activity has taken place since the attack on Friday", said Commander Dean Haydon, head of London police's Counter Terrorism Command.
Authorities searched a home in the London suburb of Stanwell, also neighboring Heathrow Airport, that was linked to the second suspect, who was not identified.
The arrests were carried out by officers from the Met's Counter Terrorism Command, supported by colleagues from Gwent Police and the Welsh Extremism and Counter Terrorism Unit (WECTU).
Steven Griffiths, 28, who lives opposite elderly foster couple, said: "When I saw the blacked-out van and the guns, I thought that this wasn't a little thing".
"I said to my mum: 'They are going in to kill".
"All I know is that they gave up the fostering and someone got in touch with them and they started taking kids again, refugees, about a year ago".
"I'm sorry! I'm sorry!" he allegedly yelled as undercover cops pinned him, causing a pile of Kit Kats and chocolates to spill out of his bag, the paper reported. Officials say 30 people were injured, including some hurt in the panic that ensued, and all but one have been released from the hospital.
The first suspect was arrested at around 7.50am, in the port which is the busiest ferry hub in Europe and serves as a commercial gateway to the French coast, including Calais and Dunkirk.
The two suspects were both arrested on Saturday.
The teenage suspect arrested in Dover is understood to be an Iraqi orphan who had moved to Britain aged 15 after his parents died, a local politician said.
Leader of Spelthorne Borough Council Ian Harvey, whose ward is Sunbury East, said he learnt about the boy's background from neighbours of Mr and Mrs Jones and information available publicly.
Mr Vaselicu, who was forced to hang around the area after his auto was seized on his way into Britain, told the Press Association: "We were in the seating area at the terminal, the police were interrogating this guy for around 10 minutes".