UK police in militant attack exercise
Police in London have simulated a militant attack on a shopping centre in an annual exercise to keep firearms officers up to speed.
It's an exercise held annually but this year has greater significance in the wake of the Paris massacre.
Assistant Police Commissioner Patricia Gallan said the Paris attacks had already led to changes.
"Paris means yet again we realise how close the terrorist threat is. We've reviewed out tactics as we do after every single terrorist incident, we've increased the number of armed response vehicles we have on the street and we continue to train our officers to be ready and aware and alert."
The exercise was intended to help keep the force of about 2, 000 firearms officers fully trained and ready for all scenarios.
It was also meant to help reassure the public the nation's security forces are ready to deal with such attacks on British soil.