Internal fire doors

Hi after some advice.

I work in housing and I have a 3 storey block of flats 1970’s built.

A resident has taken the internal doors  off the hallway to all rooms.

The resident is adamant they were not fire doors. I am sure if built in the 70’s the doors to the hallway would have been. So if the case they can not be non worsening under building regs and would need to be replaced like for like.

My other point is that even if they weren’t fire doors they should be replaced to the current standard ADB table C1 says FD20.

I may note as-well the resident is on the second floor. I know if on ground and first if and floor <4.5m the internal hallways do not need to be fire doors if a window escape is available in all habitable rooms.

My issue is the resident is going to be billed as they removed the doors without consent, so as you can imagine he is really fighting me on this. He is adamant the doors were standard doors to living room and bedrooms but thinks kitchen was FD. 

Please prove me right that all the doors need to be FD20 minimum FD30  for bedrooms, living room and kitchen.