Building Regulations specify that in homes over two storeys high, every door of a habitable room leading to a stairwell must be a fire door (this does not apply to toilets or bathrooms). Fire doors are also required between the house and integral garage (if applicable).
In non-domestic buildings, there must be a protected escape route; making fire doors essential in rooms that lead to corridors and stairwells.
However, we recommend you consult the latest Building Regulations if you’re unsure.