LONDON (Reuters) - British police hunting those behind a bomb which injured 29 people on a London train on Friday said they had arrested an 18-year-old man in a small town outside London on Saturday.
“We have made a significant arrest in our investigation this morning,” Neil Basu, Senior National Co-ordinator for Counter Terrorism Policing, said in a statement. “Although we are pleased with the progress made, this investigation continues and the threat level remains at critical.”
The man was arrested under the Terrorism Act in the southern port area of Dover.
Prime Minister Theresa May put Britain on the highest security level of “critical” late on Friday, meaning another attack may be imminent, and deployed soldiers and armed police to strategic sites.
In what police called a “significant” development, at about 7.50 a.m. officers arrested a man in Dover, from where passenger ferries sail to France. Five hours later they raided a property in Sunbury, a commuter town southwest of London, and evacuated nearby premises as a precaution.
Pictures on social media showed police in a nondescript residential street in Sunbury, in the county of Surrey.
“This arrest will lead to more activity from our officers,” said Neil Basu, speaking before details of the Sunbury raid was confirmed. “For strong investigative reasons we will not give any more details on the man we arrested at this stage.”
In what was the fifth major terrorism attack in Britain this year, the home-made bomb shot flames through a packed commuter train during the Friday morning rush hour in west London but apparently failed to detonate fully.
The militant group Islamic State claimed responsibility.
According to media reports, the bomb was attached to a timer, unlike other recent blasts which have typically been suicide bombs.
Pictures showed a slightly charred white plastic bucket with wires coming out of the top in a supermarket shopping bag on the floor of a train carriage.
The Parsons Green station where the attack took place reopened by Saturday morning.
Armed police patrolled the streets of London near government departments in Westminster and were expected to guard Premier League soccer grounds hosting matches on Saturday, including the national stadium at Wembley.
Cressida Dick, Britain’s top police officer, sought to reassure the public and tourists as she joined colleagues patrolling the entertainment and cultural district on the south bank of the Thames.
“Yesterday we saw a cowardly and indiscriminate attack which could have resulted in many lives being lost,” she said. “London has not stopped after other terrible attacks and it will not stop after this one.”
CRITICAL THREAT LEVEL
The last time Britain was put on “critical” alert was after a suicide bomber killed 22 people at a concert by the American singer Ariana Grande in Manchester in May.
The threat level remained at the highest setting for four days while police raced to establish if the man had worked alone or with the help of others. Prior to that it had not been triggered since 2007.
Prime Minister May said the public should not be alarmed by armed officers on the streets, a rare sight in Britain. “This is a proportionate and sensible step which will provide extra reassurance and protection while the investigation progresses,” she said in a televised statement late on Friday.
The bomb struck as passengers were traveling to the center of the British capital. Some suffered burns and others were injured in a stampede to escape from the station, one of the above-ground stops on the Underground network. Health officials said none was thought to be in a serious condition.
“I was on the second carriage from the back. I just heard a kind of ‘whoosh’. I looked up and saw the whole carriage engulfed in flames making its way toward me,” Ola Fayankinnu told Reuters.
“There were phones, hats, bags all over the place and when I looked back I saw a bag with flames.”
Islamic State has claimed other attacks in Britain this year, including two in London and the Manchester pop concert.
Western intelligence officials have questioned similar claims in the past, saying that while Islamic State’s jihadist ideology may have inspired some attackers, there is scant evidence that it has orchestrated attacks.