They do but your old doors were already there and don't have glass in them
so, according to the letter of the law(!), with a door closer they will do
(as my 6 panel doors did). Any new doors have to be fire doors (in areas
where bilding regs demand them, eg opening on to escape from a loft
conversion)

So... Existing door at foot of boxed in stair in hallway. Wall between
kitchen and hallway to be removed and so boxed-in stair (and door)will be in
kitchen. I intend to half-hour fireproof boxing-in and I guess, from what
you say, I need to replace the door as well...

Colin