The fuel system on a CE-marked boat is built to ISO 10088. It's the European counterpart of ABYC H-24 and H-33, covering petrol and diesel in one standard.
What it covers
The scope as published by SIS: requirements for the design, materials, construction, installation and testing of permanently installed fuel systems for internal combustion engines. It applies to all parts of permanently installed diesel and petrol systems, "from the fuel fill opening to the point of connection with the propulsion or auxiliary engine(s)", on inboard and outboard craft. The design and testing of the tanks themselves are left to ISO 21487.
What surveyors check against it
Follow the fuel from the deck fill to the engine. Check fill and vent hoses, the supply line and its hose markings, every clamp and joint, valves and filters. Smell for fuel. Look at the tank where you can see it, its fittings and its supports. See fuel hose type and age and fuel tank corrosion.
On petrol boats, check siphon protection where the line runs below the tank top; see missing anti-siphon valve.
Citing it in a finding
"Replace the cracked fill hose with marked marine fuel hose, ISO 10088." For a leak on a petrol boat, open with "do not run the engine".