Dialling 55 will connect callers to the police, who then ask questions that can be answered silently. It does not automatically dispatch police.
A viral image on Facebook of a flyer reads "If you're in a situation where you can't speak - choking, heart attack, domestic violence, intruder, etc - Ring 999. When they answer, press 55. This tells them that you need help, but can't speak. They will dispatch police to you! Worth knowing!" While this feature of emergency services does exist, it requires some interaction, which would make the service inappropriate for someone who cannot interact at all with an operator. It also does not automatically dispatch police to a caller.
Since 2001, a service called Silent Solution has made it possible for people who call emergency services to get help in situations where they cannot speak. After dialing 999, the operator asks whether the caller needs police, fire, or an ambulance. If they receive no response, they will prompt the caller to either dial 55 or make a noise, like a cough or tapping the headset, acknowledging that they need help but cannot speak. Callers can also dial 55 at any time before being prompted.
Callers are then transferred to the police, who ask a series of questions. The National Police Chiefs Council told Full Fact that, “Call handlers are highly trained to seek details from callers who may not be in a position to speak and so can use methods like tapping the handset or asking questions requiring only a yes or no answer.”
So while it is true that dialling 55 can bring police, it does require more interaction from callers than simply dialling 55. It does not automatically track the callers' location nor send police to callers. This makes it inappropriate for people who are choking or having some other kind of medical emergency that prevents them from speaking, as they might be unable to interact with the police and give yes or no answers.
Pressing 55 only works on mobile phones, and does not work from landlines. However, if callers ring 999 from a landline, hang up, and then pick the call back up within 45 seconds, the call will still be connected. Calling from a landline automatically gives police information about a caller's location.
The aim of the Silent Solutions service is to filter out accidental or prank emergency calls while still being able to help callers in situations where they cannot speak.