Hello - I'm planning on fitting some fire strips on the bedroom doors of a property that I rent out. Could you please tell me if I need to fit the strips to the bottom of the door or if just fitting them around the other 3 sides is adequate?
Thanks in advance for any advice.

The chance are, if the doors are well fitting you do not need to fit any seals but it depend on your fire strategy.

Are you considering intumescent strips, they only need to be fitted to both sides and the top of the door, however if you have substantial well fitting doors then you may not require them at all.

If you are considering cold smoke seals they need to be fitted to both sides, top and threshold but this will depend how your domestic smoke detectors are located, if they are located in the escape route then smoke has to percolate pass the doors from habitable rooms to operate the smoke detect in the corridor or hall, if they are in every habitable room and interlinked then you could fit cold smoke seals.   

If it's a House of Multiple Occupation then the rules are reasonably strict, however if you are renting out a house as a single unit to a single family then as long as the existing doors are in good condition and fit well in the frame any money you have set aside for fire safety would be better invested in the installation of decent automatic fire detection such as hard wired or radio linked smoke alarms to at least the circulation areas and if you want to be really robust the living room and a heat alarm in the kitchen as well.

If it is a HMO then the LACORS Guide http://www.rla.org.uk/docs/LACORSFSguideApril62009.PDF will be of use as well as your local Council's Environmental Services (who many have local minimum specifications for HMO's that reach the threshold for licensing)