They are intended to help emergency services practise their plans against serious attacks, such as those in London and the Manchester Arena in 2017, and to experience working together under extreme conditions. Steven Moore, head of emergency preparedness and specialist operations for EEAST, said: “The Papworth site, which is closed to the public, allows us to train in conditions as realistic as possible. “The exercises include smoke, simulated gunfire and actors playing casualties with very convincing wounds.

“After recent events, blue light services can’t have the luxury of believing that some situations are unthinkable. “We have to work together and be as prepared as possible for when the unthinkable happens.” The exercises were carried out through the Joint Emergency Services Interoperability Programme (JESIP).

Similar training exercises ran last year, successfully training around 1,500 emergency responders. This year there were 20 training days. A joint statement from Bedfordshire, Cambridgeshire and Hertfordshire Constabularies said: “The exercises have provided an invaluable platform to allow armed officers to train in a realistic operational setting with other emergency service responders.

“This real-world training is essential to prepare officers in the event of a live incident. “We have also been able to include unarmed local policing officers and all of our Tactical Firearms Commanders in the training, giving them a unique insight into JESIP workin.