In reply to UKC News: Do be aware that the reply I got from the people who run this service, when asked about MR type incidents stated:
"Firstly, as it uses SMS, delivery of messages cannot be guaranteed and secondly, it is necessary to send a number of messages before help is sent. The last point is very important because people imagine that if one SMS message gets through, help will be on its way. This is not true as the emergency services need to ask questions about your location and the nature of the problem. If the emergency service does not receive a response to their questions, no action will be taken. This exchange of SMS messages means that making a voice 999 call will always be quicker.
If you are situated in the mountains where the mobile coverage is patchy and there is a likelihood that only one message will get through, I would always suggest sending an SMS message to someone who knows you, your route, and can contact 999 on your behalf."
Denzil OMRT