Theresa May has this week increased the terror threat level to critical, warning that another attack could be imminent.

Although media have not received information of a threat in a specific location and do not wish to cause undue alarm, now seems like a useful time to remind people of the British police force’s Silent Solutions procedure.

The simple process allows a person to call police or other emergency services in circumstance where it may not be safe to talk outloud or make a noise.

Here’s how to place an emergency call when you’re scared to speak...

When you call 999, an operator asks which emergency service you require before rerouting the call to the police, ambulance service or fire brigade.

If a 999 caller doesn’t talk, the operator will ask them to cough or make another audible sound.

In certain situations, it may not be safe to make a noise – for example it could alert a potential attacker to your exact whereabouts.

Emergency services simply don’t have the resources to investigate every call made to 999 during which no sound is made.

Although there’s a simple way of signalling that it’s a genuine emergency and you haven’t just accidentally pocket-dialled.

You simply dial 55.

The procedure is called Silent Solutions and it was created so people in an emergency can call the police in dangerous situations.

After you dial 999 and you’ve been unable to audibly signal to the operator, your call will be forwarded to an operating system.

If you’re in danger, dial 55 otherwise the call will be terminated.

The ‘55’ Silent Solution protocol has been in place for over a decade, although police have recently issued a reminder as not many people know about the protocol.