PPS 3 Access Movement and Parking·Page 17·5.6
Access provision for existing buildings open to the public
For alterations or changes of use to existing buildings open to the public, suitable access for all should be provided as far as reasonably possible, recognising that level access may not always be achievable.
It is recognised that many existing buildings were not designed with disabled people in mind. Accordingly it may not always be possible for development involving the alteration or change of use of an existing building which is open to the public to provide level access. In such cases there will be a presumption that suitable access for all should be incorporated as far as reasonably possible. Designing suitable access in these circumstances may call for imagination and creativity.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 3 - Access Movement and Parking.pdf