A TOP Avon and Somerset police officer is urging the public to help combat terrorism after revealing how one phone call helped prevent an atrocity with "mass fatalities".

Chief Inspector Matt Iddon said a tip-off from a member of a mosque who had become suspicious of another man's activities triggered one of the force's biggest-ever operations.

Officers raided Andrew Ibrahim's Westbury-on-Trym flat, where they discovered explosives he had stockpiled as part of a plan to blow up a Bristol shopping centre.

He was jailed in 2009 for preparing terrorist acts DCI Iddon said: "Ibrahim intended to carry out explosions which would have led to mass fatalities, so that single phone calls undoubtedly saved many lives."

He was speaking during a podcast at Monday's launch of Counter Terrorism Policing's Action Counters Terrorism (ACT) campaign, supported by Avon and Somerset, to encourage people to help tackle terrorism.

"The importance of the information provided to us by the community, particularly in terrorism-related cases, cannot be understated," said DCI Iddon.

"The public are one of our most vital assets and without their eyes and ears acting on our behalf we would not be half as effective as we are in preventing criminality of all types."

People across Somerset are being urged to act on their instincts to beat the terror threat.

With terrorism becoming increasingly complex and varied, Counter Terrorism Policing has teamed up with Avon and Somerset and other forces calling on communities to help prevent attacks in the UK and overseas.

The appeal comes as new figures reveal information from the public has assisted counter terrorism police in a third of their most ‘high-risk’ investigations.

Launching ACT at a time when the threat remains 'severe' - meaning an attack is highly likely - Assistant Commissioner Mark Rowley said: "It is very encouraging that in a third of cases involving our most serious terrorist suspects we have benefited from information from the public.

"The number of calls and online reports we receive is also increasing.

"This is a testament to the trust people hold in policing - but now we are appealing for even more.

“Counter terrorism policing and the security and intelligence services are working tirelessly to keep the public safe and together we have stopped 12 attacks since the summer of 2013.

"However, advances in technology make it more complex and challenging for us to spot would-be terrorists because it's easier for them to be in contact with others and be radicalised in a relatively short space of time using encrypted communications.

“The threat is becoming more varied and the move towards low-tech attacks on crowded places, like those we have seen in major European cities and beyond, makes it even more important everyone remains vigilant and acts, by calling us confidentially, if they are concerned about suspicious activity.”