You need to ensure the layout complies with the granted Fire Cert, or at the very least complies with TGD Part B (Fire Safety).
Typically, once you can get the bedroom to open into the protected hallway, use of fire doors, extension of fire alarm and detection system, it can work.
Typically, Planning will be exempt as Section 41H should prevail here.
You should notify the MC that you are getting some work done, they may require a report from a Chartered Engineer stating that the works will not effect the structure of the builder, no new structural elements are being put in place and that the new works will comply with Part B (Fire Safety), that's what we done as Engineers when engaged by a city centre resident.
You may find it difficult moving the kitchen though, as you have to get all the services and waste back to the existing service duct where the kitchen is now.