Counter-terror drill in capital
A major counter-terrorism exercise is being carried out in London to ensure emergency services are ready "should the worst happen", Metropolitan Police Commissioner Sir Bernard Hogan Howe has said.
A mock terrorist firearms attack is being staged in the capital today to test the response to a Tunisian-style mass shooting.
Officers, emergency services, soldiers and intelligence officials are taking part in the operation.
Sir Bernard said: " With events like today we are committing around 1,000 people to exercise our plans and make sure that should the worst happen we are ready. And we will be."
He said the rate of arrests for terror offences has increased in the last year.
"It is clear during that time that we've disrupted some very serious plots and some of those cases are going to the courts. The reason we have exercises like today is because, obviously, we are concerned there are people planning terrorist events.
"We intend first of all to stop them from getting to attack. But should we not stop the terrorists in their planning, it's essential we disrupt them in any of the attacks that may take place.
"With events like today we are committing around 1,000 people to exercise our plans and make sure that should the worst happen we are ready. And we will be."
Preparations for the exercise began around six months ago and events such as the Charlie Hebdo attack in Paris and the hostage siege in Sydney influenced the test .
The Mumbai attack in 2008 also featured in the planning.
Scotland Yard stressed the test was in no way connected or prompted by the massacre in Tunisia last week.
Sir Bernard said: "Today's exercise will test our people in how to respond to a terrorist threat and we will learn from the mistakes that we are bound to make today.
"It's best we make them today in an environment where we don't have terrorists, than make those mistakes when we do."
The two-day exercise will see a test of the emergency service response to an attack at the disused Tube station at Aldwych.
The vast majority of police officers involved have no idea about the venues or what is planned. Only around 12 people knew specific details of in advance.
Among those taking part are all of London's emergency services, Greater London Authority, Transport for London, Home Office, Cabinet Office, Ministry of Defence, the Department of Health and NHS England.
Surrey Street will be shut for the day in order to minimise disruption.