Counter-terror police London
Counter-terror police London rehearse their response to a gun attack in JuneGetty Images

The National Counter Terrorism Security Office (Nactso) has released advice on what to do if a Paris-style gun and bomb attack is launched in the UK. The office recommends escaping if possible or finding a safe place which can be secured from entry.

In the wake of the attacks in the French capital in which 129 people were killed in shootings and bombings in bars, cafes, a concert venue and a sports stadium, Nactso recommends that victims should: "Escape if you can" after considering if there is a "safe route" and "leave belongings behind".

In Paris, survivors of the Bataclan theatre massacre in which 89 were killed have described how they were forced to lie still fearing they would be killed if they broke cover and tried to exit. In situations where running is impossible, Nactso recommends victims "find cover from gunfire", but warns "if you can see the attacker, they may be able to see you."

It advises "find cover from gunfire, for example, substantial brickwork/heavy reinforced walls" as "cover from view does not mean you are safe, bullets go through glass, brick, wood and metal."

It advises to "be quiet, silence your phone" and to barricade or lock yourself in, and if it is possible to safely make contact with emergency services, to report the location of attackers, the number of casualties, and whether they have hostages.

The document advises businesses to have a "dynamic lock-down" contingency plan in case of an attack, and to train staff to raise the alarm, and lock down a building.

"Dynamic lock-down is the ability to quickly restrict access and egress (exits) to a site or building (or part of) through physical measures in response to a threat, either external or internal," said Nactso, a branch of the national police chief's council.

In June, 1,000 police officers rehearsed their response to a terrorists gun attack on the streets of London. The current threat level for terror attacks in the UK is severe, meaning an attack is highly likely.