Armed troops have been stationed around key points in London as the UK terror alert is raised to critical.

Military forces are stationed at static posts such as at Parliament, Downing Street, and Buckingham Palace following the Manchester bomb attacks.

Defence Secretary Sir Michael Fallon told Sky News that additional troops could be deployed at locations such as Twickenham and Wembley.

Sir Michael said: "We have additional troops in reserve if the police need additional help with patrolling itself, they've not asked for that at the moment, but if they do want troops out there on patrol with them, in our town centres, our railway stations, at sporting events, then of course we are ready to help and we have troops trained to do that."

He emphasised that the deployment was "being done at the request of the police, and troops will always be under the direction of the police".

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Metropolitan Police Commissioner Cressida Dick said: “After the terrible events in Manchester, the raising of the threat level to critical, as you know, we have been granted military support.”

Speaking just yards from where Pc Keith Palmer was murdered outside Parliament in March, Ms Dick said: “The military are here and a number of locations in London in order to allow us, the police, to put more armed officers on the streets to support the public, and to protect the public and to protect events.

“As soon as we no longer need our military colleagues, we will be saying so and we hope that the threat level will reduce from critical.

“When it does, clearly there will be a de-escalation requirement for military colleagues but I am not going to put a timescale on that.

“I think the vast majority of the public will be utterly reassured to know that... we have the ability to call upon and have called upon the military in this way, and actually we now have more armed police officers out on the streets.”

However Steve White, chairman of the Police federation, warned that the deployment of military personnel to the UK's streets highlights the fact the police don’t have the numbers to manage events like this.

The Police Federation, which represents 120,000 rank and file officers in England and Wales, has warned said that workforce figures released in January show that more than 2,700 officers left the service in the 12-month period ending September 2016 - the largest drop for the past three years.

Mr White said: “The welcome support of the military to free up armed officers and offer public reassurance will no doubt be managed in the same professional, resolute way.

“But, as welcome as this is, we cannot avoid the reasons it is needed at all.

“There is no ignoring the fact that we, the police, simply do not have the resources to manage an event like this on our own.”