In my view it most certainly does apply. It fits within the definition of a Premises. There may be 'relevant persons' on the premises (e.g. estate agents showing people round)? There may be relevant persons off the premises (e.g. neighbours). Fire-fighters may have to carry out their duties in the premises so there might be obligations under Regulations 37 and 38.
You might argue that in an empty premises there is no fire risk to any occupants of that premises, but the Order requires you to cast your eye beyond the premises by including "...any person in the immediate vicinity of the premises who is at risk from a fire on the premises...". You might even argue that with respect to neighbours etc an empty premises might be regarded as a higher risk in certain circumstances (arson & poor maintenance could be examples).
Not sure about case law (I'm no lawyer)!
