A disused Tube station was the scene of a simulated terror attack yesterday as police and emergency services responded to reports of shots fired by a group of men who disappeared into the underground network.

The major counter-terrorism exercise shows that police and other agencies are ready to face any threat "should we need to", said Metropolitan Police Deputy Assistant Commissioner Maxine de Brunner.

The large-scale training exercise came five days after at least 30 Britons were killed when a gunman attacked holidaymakers on a beach in Tunisia.

While this exercise was planned months before Friday's attack, Ms de Brunner said it is likely the massacre could inform future training for emergency services.

Events including the Charlie Hebdo attack in Paris, the hostage siege in Sydney and the 2008 Mumbai attack influenced the test.

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Asked about Tunisia Ms de Brunner said: "It is likely that it could be (taken into account) by a future exercise director."

She was keen to stress that no specific intelligence had informed the two-day exercise, which continues tomorrow.

The disused Tube station was chosen, she said, because it is a live venue and being able to close the entrance at Surrey Street minimised disruption to the the public.

Paramedics and fire officers could be seen carrying casualties, played by actors, out of the station on stretchers while sirens wailed in the surrounding streets in Aldwych.

The majority of those taking part had no idea what they would face during the exercise.

Ms de Brunner said: "What it shows is that we are ready in the event of an attack and that we are testing ourselves and we are testing our interoperability with other agencies and where we don't get things quite right, that we take that learning and we try to be as good as we can be in the event of anything coming to London."

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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.

As temperatures hit the high 20s officers could be seen with water bottles in their vests.

The participants were briefed beforehand and advised to drink plenty of water and ensure they had eaten in order to cope with the heat.

While the exercise is a simulation only, the emergency services were treating it very seriously, said London Ambulance Service's director of operations Jason Killens.

"Once they get to the scene where the patients are and those patients are made up with simulated injuries it becomes very real for them and the training kicks in," he said.

Metropolitan Police Commissioner Sir Bernard Hogan Howe earlier said the rate of arrests for terror offences has increased in the last year.

He said: "It is clear during that time that we've disrupted some very serious plots and some of those cases are going to the courts.

"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."

Police said later that the exercise, called Operation Strong Tower, had been going on for eight hours.

During the afternoon officers and emergency services colleagues were called to deal with a number of people being held hostage. This scenario developed into a siege that ran for about six hours.

Throughout the exercise senior staff from all the London agencies and Government were tested in their decision making and consequence management, Scotland Yard said.

The afternoon phase of the incident was played out at a disused building on the Albert Embankment, Lambeth.

The exercise continued throughout the night.