I'm prompted to post this after receiving yet another of those bulk e-mails about emergency phone calls which is full of misleading information and appears to have been part written by somebody who knows nothing about the subject and part translated from a North American original which in itself is a dubious story to begin with.
I'm pretty sure most of these points have been made elsewhere before in various threads, but I'll collect them here together for reference.
Myth #1. You can use 911 in the U.K. as an alternative to 999.
False. It's possible that an office PBX somewhere has been programmed to accept 911 and translate it to the British 999 on an outside line, and it's even possible that there might be an obscure cable or VoIP system somewhere which does a similar translation, but as a general rule 911 will not work in the U.K. In fact in one or two areas 911 can now be the first three digits of a normal local number. Trying to use 911 in Britain will just waste valuable time in an emergency.
Myth #2. Keep an old mobile phone in your car without a SIM card just for emergency use. You can still dial 999 on it even though it won't make any other calls.
False. I assume that this myth has arisen through a misunderstanding. The GSM phone specification requires that the phone must attempt to make an emergency call even without a valid SIM card. Whether the call will succeed, however, depends upon whether any network will accept such an unidentified call. None of the U.K. networks will. Trying to make a 999 call without a valid SIM card in the U.K. will result in the phone attempting to connect and then just reporting "No network coverage."
Myth #3. If you are alone on the road and think a police car trying to stop you might not be genuine, use the new 112 number instead of 999 to save time. This will connect you directly to the local police.
False. 112 was introduced under EU regulations a few years ago to operate as an additional emergency number alongside our traditional 999. Dialing 112 in the U.K. (from a mobile phone or a landline) just connects you to exactly the same place as 999 and you will get the operator asking you which emergency service you require.
And a related one.....
Myth #4. Use 112 from your mobile phone instead of 999, because it will connect you directly to the local police even if you have no signal to make a 999 call.
False. How on earth this myth got started I have no idea. There is nothing "magic" about dialing the number 112 on your cellphone. It's handled in exactly the same way as 999, so if you have no signal available to let you dial 999, then you will not be able to dial 112 either. No signal is no signal.
Myth #5. You can dial *77 / #77 / *677 / some-other-code to reach the motorway traffic police for a road accident.
These don't seem to appear quite so often in supposedly U.K.-specific stories, but I've seen a few. They are clearly adapted from North American reports where states variously use *HP for Highway Patrol, *SP for State Patrol, etc. from cellphones. The *677 number originates from Canada, specifically Ontario where *OPP is for the Ontario Provincial Police.
There are no separate, distinct emergency numbers in the U.K. for traffic police such as these. In an genuine emergency on the highway, you should use the standard emergency number 999 (or 112).