Hey Clayton,
Yes, seen that extract from the Whitebook but it’s only available at the Irish domain BG site even though it refers to British Standards.
UK BG have effectively told my local authority Building Control that they only have test data for 195mm joists.
The UK BG site is %@$&*!#.
My local authority Building Control is not budging at the moment, however, a private company I approached has confirmed that they will accept any structurally justified joist with the fire resistant lining installed below.