An armed police operation is under way by counter-terror officers investigating the Parsons Green bombing.
A house is being searched and residents close to the address in Sunbury-on-Thames, Surrey, are being evacuated, Scotland Yard said.
The raid comes after the arrest of an 18-year-old man in Dover earlier on Saturday who is understood to be the suspected bomber. The arrest was described by Deputy Assistant Commissioner Neil Basu as “significant”.
The evacuation in Sunbury began at 1.40pm following the arrest at 7.50am. Scotland Yard said it was “a precautionary measure following the arrest of a man in Dover”. A 100-metre cordon is in place.
Speaking after a meeting of the Government’s emergency Cobra committee, Home Secretary Amber Rudd said the arrest was “very significant”, but added: “The operation is ongoing.”
Investigators – who it is understood are linking the attack to Islamist extremism – are continuing their probe and the threat level remains at critical, which means a further attack is feared to be imminent.
The country’s top counter-terrorism officer indicated that a potential network of plotters could have been involved. Assistant Commissioner Mark Rowley said police were “chasing down suspects”, while suggestions were made by Donald Trump that the bomber was known to Scotland Yard.
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The suspect has been arrested under section 41 of the Terrorism Act 2000. This gives police the power to arrest someone suspected of terrorism-related offences without a warrant.
These powers allow the extended detention of suspects without charge beyond the maximum four days available under the law that governs most other arrests.
His capture took place in the port area of the city, which is the busiest ferry hub in Europe and serves as a commercial gateway to the French coast, including Calais and Dunkirk.
A key strand of the investigation has focused on CCTV as officers comb through footage to establish who planted the device, and when and where it was placed on the train.
Security minister Ben Wallace suggested CCTV images of the bomber could be released as part of the manhunt for those responsible, but Scotland Yard subsequently denied there were any plans to do so.
The suspect is expected to be moved to a south London police station.
Met Police Deputy Assistant Commissioner Neil Basu (Lauren Hurley/PA)
Mr Basu said: “We have made a significant arrest in our investigation this morning. Although we are pleased with the progress made, this investigation continues and the threat level remains at critical.
“The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation. We are not, at this time, changing our protective security measures and the steps taken to free up extra armed officers remain in place.
“This arrest will lead to more activity from our officers. For strong investigative reasons we will not give any more details on the man we arrested at this stage.”
A police forensic tent next to the train. (AP)
A vast manhunt was launched after an improvised device partially exploded on a District Line train at Parsons Green station during the Friday morning rush hour, injuring 30.
Three victims remain in hospital, NHS England said.
Troops have been dispatched to key sites across the country to free up armed police officers after the country’s terror threat level was raised to its highest point.
The force said it has spoken to 45 witnesses and 77 images and videos have been sent to detectives by members of the public.
Passengers pass a police officer at the entrance to Parsons Green station. (PA)
Friday’s device reportedly contained the explosive triacetone triperoxide (TATP) and nails, but is thought to have only partially detonated from inside a bucket.
Parsons Green station was reopened in the early hours of Saturday.
There were fears the number of those hurt could have been much higher – with the real potential for life-threatening injuries – had the bomb, which was concealed within a supermarket carrier bag, fully exploded.
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It is not yet known whether the bomb, which was reportedly fixed with a timer, went off at its intended target.
The train – bound for Edgware Road – was just pulling into the station in south-west London when the device detonated in the rear carriage, sending passengers fleeing to safety.
Speaking after a meeting of the Government’s emergency Cobra committee, the Home Secretary said: “This is a very significant arrest, the police have made very good progress, but the operation is ongoing and we will have to wait to hear from them about any more information.”
Asked about whether the bomber was part of the current security picture, Mrs Rudd said: “I think it is much too early to say that, we have one arrest and an ongoing operation – when we have more information, we will be sharing it.”