The building regulations give the definitions below and since they state a nursing home is an "institution" by default it cannot be a dwelling.
Additionally APD P states:
Part P applies to electrical installations:
a. in a dwelling-house or flat, [and outside and in additional buildings]
b. in the common access areas of blocks of flats such as corridors and staircases
c. in shared amenities of blocks of flats such as laundries, kitchens and gymnasiums
d. in business premises (other than agricultural buildings) connected to the same meter as the electrical installation in a dwelling – for example shops and public houses below flats.
“building” means any permanent or temporary building but not any other kind of structure or erection, and a reference to a building includes a reference to part of a building;
“dwelling” includes a dwelling-house and a flat;
“dwelling-house” does not include a flat or a building containing a flat;
“flat” means separate and self-contained premises constructed or adapted for use for residential purposes and forming part of a building from some other part of which it is divided horizontally;
“institution” means an institution (whether described as a hospital, home, school or other similar establishment) which is used as living accommodation for, or for the treatment, care or maintenance of persons—
(a) suffering from disabilities due to illness or old age or other physical or mental incapacity, or
(b) under the age of five years,
where such persons sleep on the premises;
“room for residential purposes” means a room, or a suite of rooms, which is not a dwelling-house or a flat and which is used by one or more persons to live and sleep and includes a room in a hostel, an hotel, a boarding house, a hall of residence or a residential home, but does not include a room in a hospital, or other similar establishment, used for patient accommodation;
“public building” means a building consisting of or containing—
(a) a theatre, public library, hall or other place of public resort;
(b) a school or other educational establishment not exempted from the operation of building regulations by virtue of section 4(1)(a) of the Act(b); or
(c) a place of public worship;
but a building is not to be treated as a place of public resort because it is, or it contains, a shop, storehouse or warehouse, or is a dwelling to which members of the public are occasionally admitted.