This excellent tip from the Dinghy Cruising Association forum:
"The mobile phone companies can triangulate your position if you dial 112, and so get (and give the operator) a rough fix on where you are. The 999 system is not set up to do this. If you dial 999 from a mobile the operator has no idea where in the UK you are until you tell them."
This is particularly important if you want to get in touch with the coastguard, who will be able to alert the right lifeboat station as soon as possible.
This is an admirable service!!!
After I first registered for this service (nearly 3 years ago) and found out the benefits I informed various club committee and ordinary members of this, in the hope that the info would be broadcast.
The best introduction to this service that I have found was (and I think still is) on this link to a videoclip...