The number of firearms officers available across Hertfordshire, Bedfordshire and Cambridgeshire has been increased by 50 per cent, in line with moves initiated last year.

The Beds, Cambs and Herts joint protective services set about increasing the number of authorised firearms officers in July 2016, “to help protect the public and respond quickly to serious threats”.

Police said the increase was not in relation to any recent terror attack or specific intelligence regarding any imminent terror threat, but followed a direction made to all forces last year by the Home Office.

A spokeswoman added that the exact number of firearms officers could not be disclosed for national security reasons.

Paul Fullwood, the unit’s assistant chief constable, said: “The terrible and tragic terror attacks in Manchester and London are a timely reminder of just why this increase is needed, although I’d like to stress that this increase has been planned for several months and is not in relation to any specific intelligence.

“Last year we carried out a review of the tri-force armed policing unit and found that the number of firearms officers across the three forces was sufficient to meet our day-to-day demand, but we felt it would be beneficial to increase the number of officers who are firearms-trained in order to provide the best possible levels of protection and security across the three counties.

“Since then we have carried out a series of intensive training courses to ensure we have the very best calibre of people in this high-pressured role.

“When others run away from danger, our brave authorised firearms officers run towards the threat, as has been seen this weekend.

“They’re often faced with difficult and challenging decisions, and as such we are hugely appreciative of their efforts in keeping the wider public safe – and I am grateful to our officers who have volunteered to be part of this uplift.”

The officers have been chosen from among those already working within the joint protective service unit. They will not carry weapons routinely, but are ready to be called on in exceptional cases such as those where lives are at risk.

The UK terror threat level remains at severe, meaning an attack is thought to be highly likely.

Seven people were killed and 48 injured in Saturday night’s London Bridge attack. The perpetrators – named as Khuram Butt, Rachid Radouane and Youssef Zagha – were shot dead by police within eight minutes.

That attack came after May 22’s Manchester Arena suicide bombing – which saw 22 people killed and 116 injured – and the attack on Westminster on March 22, when four pedestrians and hero PC Keith Palmer lost their lives, with 49 others injured.