From the government planning portal ...
If a bathroom or kitchen is to be provided in a room where there wasn't one before, building regulations approval is likely to be required to ensure that the room will have adequate ventilation and drainage, and meet requirements in respect of structural stability, electrical and fire safety.
All work has to be done to building regulations.
You can have a toilet off a kitchen with only a single door providing the toilet room has a sink, this was allowed from the 2012 regulation changes.