There may be a situation where someone needs help during an emergency but is unable to talk because of an abuser being in close proximity. Here they can call 999 and press 55. This is known as the Silent Solution and will let the police know there is an emergency.
With Silent Solution, a police system is used to filter out accidental or hoax 999 calls. It also exists to help people who are unable to speak, but who genuinely need police assistance. Callers will hear an automated police message, which lasts for 20 seconds and begins with “you are through to the police”. It will ask the caller to press 55 to be put through to police call management. The BT operator will remain on the line and listen. If the caller presses 55, taps or makes a noise, they will be notified and transfer the call to the police. If none of the above are done, the call will be terminated after 45 seconds.
Thames Valley Police has guidance on using Silent Solution which can be read at https://www.thamesvalley.police.uk/silentsolution.