Soldiers will be deployed in key public locations to support armed police as the UK’s national threat level was raised to ‘critical’ in the wake of the Manchester Arena terrorist bombing.
The shift to the highest threat level means that further attacks may be imminent, according to prime minister Theresa May.
Military personnel may also be seen at other events such as concerts over the coming weeks, working under the command of police officers to protect the public.
May said she did not want the public to feel “unduly alarmed” but said it was a “proportionate and sensible response”.
The change in terror threat comes after investigators were unable to rule out whether suspect Salman Abedi acted alone.
The former Salford University student – understood to be a 22-year-old born in Manchester to parents of Libyan descent – is thought to have blown himself up in the arena’s foyer shortly after 10.30pm on Monday.
The highest threat level, which is decided by the Joint Terrorism Analysis Centre – a group of experts from the police, government departments and agencies – has only been reached twice before.
The first time the threat level was raised to critical was in 2006 during a major operation to stop a plot to blow up transatlantic aircraft with liquid bombs.
Security chiefs raised it once more the following year as they hunted for the men who had tried to bomb a London nightclub, before going on to attack Glasgow airport.
The tightened security measures came as a fourth victim was named as a result of Monday’s bombing which killed 22 and injured 59 at the end of a Ariana Grande concert.
London mayor Sadiq Khan said: “There will be additional police officers on London’s streets over the coming days – including additional armed officers.
“You will also see some military personnel around London – they are there to help our police to keep us safe and guard key sites.”
Counter-terror police arrested a man at Stansted who was suspected of planning to travel to Syria.
The 37-year-old was due to board a flight for Turkey last night when he was held on suspicion of preparing for acts of terrorism.
His arrest is not connected to Monday night’s suicide bomb attack at Manchester Arena, Scotland Yard said.
Two residential addresses in north London are being searched, the BBC reported.