In the UK, it is the Maritime Coastguard Agency who are responsible for the co-ordination of any maritime incident.
If you need to report an emergency at sea or on the coast, you should do one of the following:
TELEPHONE - Dial '999' and ask for the COASTGUARD.
VHF RADIO - Channel 16 (or VHF DSC)
DISTRESS FLARE or other Distress Signal.
N.B - MOBILE PHONES should NOT be used as the PRIMARY method of reporting an incident at Sea, as they are of limited use to the Emergency Services.
The Coastguard and Lifeboats CANNOT use direction finding equipment to locate a mobile phone signal, and mobile phone signals may be unreliable at sea. There is also the risk that they will affect any navigational or any other electronic equipment carried onboard your vessel.