Part M isn'y very well worded, it should be revised this year. as for te lifts i'll try my best to decode it.
a lift must be provided in buildings that are either:
(a) a two storey building has a nett floor area
per floor of more than 280 m2; or
(b) a building of more than two storeys has a
nett floor area per floor of more than 200 m2.
the area is calculated my all areas that can be reached through the same entrance to a storey. excluding stairs, toilets and maintance areas.
A lift also has to be provided where there are more than 8 flats above or below ground.
or where there are more than two flats at a height above 10m, measured from the entrance level. (this will be 3rd floor sometimes, but 4th floor all the time)
if a lift is not required, then at least one ambulant disabled stairs should be provided.
how many storeys is the building in question.