Hi, Ive recently bought a 1920s 4 storey house, and im planning to replace the original pine doors which have been dipped and are falling apart. We are undertaking a general rennovation to the house - replastering, relocating partitions, new roof, windows, basement rennovation etc, but not sure if this all means I have to install firedoors to meet modern regulations. Any advice is welcome!

Does the work you are doing fall within the scope of Building Regulations?

The basement revovation will need to comply with buiding regulations as we require structural work, inc underpinning.

Best to check with local authority building control on fire door requirements then.  Protected escape route from upper floors, Approved document B (dwellings) Annex C Fire Doors.