Alistair,

For initial research stick with .gov and local authority stuff like this

https://www.legislation.gov.uk/ukpga/1990/9

Also look up on the LA planning portal if the property has asked for permission to do anything previously

LA planners are a fickle bunch, sensible on some stuff, stupidly stubborn on others, they get mardy and pull the 'we'll just take you to court if you do that' line...despite the fact that building control has asked for it

Jon M