Just one example: Who is the law enforcement agency for UK waters, such as a River Estauary?
1. The Police
2. The River Bailiff
3. The Coastguard
4. The Harbour Commissioner
5. The Environment Agency
6. The Local Council
7. The County Council... etc.
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As far as 'commercial' vessels are concerned, these will include Commercially endorsed RYA tickets (RYA for MCA) - 12 passengers max, Boatmaster Licencing (MCA) - up to 250 passengers, Boatmans Licencing (Public Health Act - so local authority Public Health officer) - 12 passengers max. In addition, these will also Code a vessel for operation in these specific waters.

However, the MCA still maintain authority over British flagged vessels wherever they operate. Harmonisation, has yet to be agreed, an example being the recent Boatmaster Tier 1 ( allowing operation within other EU countries), so there remains a multi-layered fog.

Additionally, foreign countries, including the EU, can require STCW 95 compliance for all crew & Master 200+ for skippers.