Room AST or Property AST?

I have a large flat, split into 4 “bedsits / studios”.

Each unit has a bed/lounge/kitchenette forming one large room plus an en-suite. Each has its own lockable entrance door.

Each unit has its own coin meter for electric consumption. None pay council tax, tv licence, water bills etc.

There is a communal area with a washing machine and a dryer.

There is one main entrance door to the flat.

Q do I issue ASTs as a flat-share by the room OR do I issue ASTs for each unit ??

Thank You