MORE than 1000 police officers, members of the armed forces, transport workers and Whitehall officials have taken part in the biggest counter-terrorism exercise the UK has ever seen.

Operation Strong Tower showed that Scotland Yard and other agencies were ready to face any threat "should we need to", declared Maxine de Brunner, the Metropolitan Police's Deputy Assistant Commissioner.

The counter-terrorism exercise represented a "marauding attack" and centred on a disused Tube station with the police and emergency services responding to reports of shots fired by a group of men, who had disappeared into London's underground network.

While the exercise took place just five days after the Tunisia terror attack, it had been planned for months in the wake of the Charlie Hebdo atrocity in Paris in January.

Asked about the Tunisia attack, 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 today.

The disused Tube station was chosen, the police chief explained, because it was a live venue and, being able to close the entrance at Surrey Street, had 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.

"We are ready in the event of an attack and that we are testing ourselves and we are testing our inter-operability 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," explained Ms de Brunner.

Among those taking part were all of London's emergency services and other key agencies. The rate of arrests for alleged terror offences has risen over the past year.