What are the two categories of British ship register under The Merchant Shipping (Categorisation of Registries of Relevant British Possessions) Regulations?

Category 1 registers, on which any ship may be registered, without restriction as to tonnage, type or length; and Category 2 registers, on which passenger ships, pleasure vessels of more than 150 tons, and other ship types which are of more than 150 tons may not be registered.