All this will not apply to people who use their boat as their primary residence (although it looks like you have to have a permanent mooring).
5.42 It is the government’s intention that people whose primary, or often their only, place of residence is their boat (which has a permanent mooring), will remain entitled to use red diesel. The government will set out what requirements these boat users need to provide to justify a continued use of red diesel, even if their craft has only one fuel tank.