RN Fishery Protection Squadron: Provides fishery enforcement in English, Welsh, and NI water, and occasionally Scottish. Does national tasking such as shadowing Russian or Chinese warships of other vessels of interests. Can be used for Military Aid to Government Departments of Military Aid to The Civil Power - as can other RN ships. MAGD/MACP can include counter narcotics, counter terrorism, SAR, anti pollution, and so on.
Marine Scotland: Performs fishery protection in Scottish waters.
Border Force: Has five cutters used for anti illegal immigration and counter drug tasks. Two are returning to the UK from Med.
Police: Virtually every UK Police force has an area of coast, and have small patrol vessels, RIBs, and can patrol/board. The Ministry of Defence Police has full constabulary powers throughout the UK, and a large fleet of launches, mostly in the naval ports.
HM Coastguard: Coordinates Search and Rescue from shore stations, provides cliff/beach rescue teams and provides SAR helicopters via contract. Also provides marine salvage and towing via a contractor.
RNLI: Provides lifeboats through the UK and Ireland, manned by volunteers.
Trinity House: Responsible for light houses, light ships, and navigation bouys in English, Welsh, and NI waters.
Northern Lighthouse Board: Does the same in the Scottish and Isle of Man coasts.