The Design Considerations in Approved Document M: Volume 2 Buildings other than dwellings 3.17 make it clear that "...a passenger lift is the most suitable means of vertical access and should be provided wherever possible. However, given the space constraints in some buildings, it may not always be possible to install the type and size of passenger lift that would be suitable for use by all, and other options may need to be considered to provide for users with mobility impairments."
Approved Document M: Volume 2 Buildings other than dwellings 3.21 and 3.22 add that "...For all buildings, a passenger lift is the most suitable form of access for people moving from one storey to another..." but emphasise that "...in exceptional circumstances for new developments with particular constraints (e.g. a listed building, or an infill site in a historic town centre), where a passenger lift cannot be accommodated, a vertical lifting platform (platform lift), although not equivalent to a passenger lift, may be considered as an alternative option to provide access for persons with impaired mobility." The Provisions at Approved Document M: Volume 2 Buildings other than dwellings 3.24 state that "...The provision of lifting devices will satisfy Requirement M1 or M2 if ... new developments have a passenger lift serving all storeys [or] new developments, where due to site constraints a passenger lift cannot be accommodated to provide access to persons with impaired mobility, have a lifting platform, of a type designed for the vertical height to be traveled"
The guidance is clear therefore that the normal expectation would be for a lift to be provided in new developments, with justifiable exceptions where a lifting platform may be acceptable. It should be noted that the situations mentioned (e.g. a listed building or an infill site in a historic town centre) are examples only. Each situation should be judged on its merits.
The aforesaid does not however mean that there will be no exceptions to these principles. The legal requirement of the Regulations is that there shall be reasonable provision for access. What is reasonable must be judged on the circumstances of the individual case, and there will almost certainly be cases where the provision of any kind of lifting device may be unreasonable.
The onus must, however, be on the applicant to justify such exceptions in an Access Statement. As an indication of the sort of factors that might be relevant to such a justification, applicants may wish to demonstrate for example that no members of the general public are accommodated, that all facilities are replicated on each floor, that the space demand of the lift and associated landings is disproportionate to the accommodation provided, that adequate provision is made for installation of a lift at a later date should it be required, and so forth.
It would not be reasonable to set out in guidance such as this exactly what combination of circumstances would justify omission of a lift, but nor would it be reasonable for a building control body to state in advance of consideration of an application that provision of a lift would not be required.