The man, who has not been named, was arrested in the ferry departure area of the port of Dover on suspicion of committing, preparing or instigating an act of terrorism after Friday’s attack in which 30 people were injured at Parsons Green station, AFP reported.
“We’re keeping an open mind around whether more than one person is responsible for the attack,” Neil Basu of London’s Metropolitan Police told reporters.
Dover’s ferry terminal was evacuated, as was a large area around a house in Sunbury, just outside London, as police conducted a search.
Residents of Sunbury quoted in British media said the owners of the house were elderly foster parents.
“I was in my house with my children and there was a knock at the door from the police,” local resident Mojgan Jamali told the Press Association. “They told me to leave. They said: ‘You have one minute to get out of the house and get away’.”
Witnesses described scenes of chaos after an improvised explosive device was detonated on a busy commuter train as it pulled into Parsons Green Station in west London during rush hour.
At least 30 people were wounded but none killed, in what was Britain’s fifth terror attack in six months.
The blast prompted Britain to raise its national threat level from “severe” to “critical,” meaning an attack is expected imminently.
Prime Minister Theresa May said troops would be deployed to key locations, with armed police seen patroling key locations on Saturday.
Erroll G. Southers, an expert in transportation security and counterterrorism and the author of “Homegrown Violent Extremism,” told Arab News that the possibility that more than one person was involved raises questions over how organized the plot was.
“What concerns me now we know that they are looking for more than one person is — is there any element of command and control in this?,” he said.
Daesh claimed responsibility for the attack late on Friday — but Southers said that has to be viewed in light of the terror group’s sophisticated “marketing” efforts.
“Why not claim an attack like this? It shows your reach outside of the span of the region you allegedly occupy. It shows some ingenuity in terms of the person that put this device together. They can say ‘we’ve got operatives in the UK that are engaging,’ and that works for them,” Southers said.
“(Daesh) are losing ground in Syria and Iraq … so by claiming an attack in London it works for them.”