UK Landlord Forum / Life

I have a self contained room in my terraced rental property which was a workshop with own front and back door. I would like to block off access to the main house and rent this separately as a small studio flat. Have any of you experienced landlords done this themselves and have any advice on what permissions are needed?
There is currently no kitchen but I can add a small kitchenette. It will have its own shower room, small entry way, separate heating and little garden area.
This is very confusing online as advice from the authorities seems conflicting and unclear. Any opinion or pointers are very welcome. Thank you.