In reply to mypyrex:
In all practical terms: no. PMR446 has limited transmission power and limited range, and there is no "channel 16" distress frequency like there is for marine VHF radio (for which you need a license).
It's basically line of sight - as is a mobile phone, but at least that's line of sight to a base station which relays your call directly to the intended recipient, rather than just some other bod who has his PMR446 radio turned on and tuned to your channel. That's not to say that you couldn't get lucky with freaky propagation conditions and manage to raise someone who could get on the phone and pass on your message to the emergency services, but it absolutely couldn't be relied on.
Post edited at 12:58