Yes, I get your point, unfortunately I can see that lawyers and courts might interpret it in quite a different way, 'you were asked to provide a landlord's report in accordance with the legislation as a competent electrician'.
Whilst I agree that what should be done is an inspection in line with periodic inspections as defined in the current edition of the wiring regs (in Scotland, that's what is required under the equivalent legislation) the plain fact is that the English legislation has defined the requirements differently, basically demanding compliance with the current regs.
This opens it up for lawyers to argue for compliance as basically that's what the law states.
I wouldn't want to be the one defending the 'custom and practice', or 'that's what they really meant' against a fancy lawyer, as they may have a better lawyer than I can afford!