Police in London will take part in an exercise to test the city's response time to gun-wielding terrorists today.

Operation Strong Tower will see emergency service staff and Government officials test their tactical responses should an attack take place in the capital.

The operation will run today (June 30) and tomorrow (July 1) and will see tactical response on the ground visible to passers-by outside the disused Aldwych underground station in Surrey Street, in the West End.

The operation - which has taken six months to plan - comes just days after the Tunisia beach massacre which has left at least 15 Britons dead.

An Eltham woman and a couple from Swanley survived.

Deputy Assistant Commissioner Maxine de Brunner, who is the Exercise Director, said: "Testing and exercising is a really important way to ensure that our plans to respond to a major incident or terrorist attack are as good as they can be.

"The exercise scenario will test our tactical response including working with our emergency services partners, containing the situation, evacuating the injured and managing a crime scene."