I'm helping out a relative with some historic tax stuff. They've needed to estimate valuations of some properties at various points in the past (specifically 1985 & 1998; NB not the usual magic March 1982 "CGT rebasing" date).
For residential properties this is as easy as going to
https://www.nationwide.co.uk/house-price-index/
and rolling back from the disposal price and date to what it'd have been at the date of interest. We've done that before and their accountant has been happy to accept that as an estimate of book cost for CGT calculations.
But one of the properties was a shop (ie commercial/retail), and I am dubious that it's sensible to use the Nationwide's residential house price index data for that.
Any idea if there's any (free!) equivalents to the Nationwide house price index data, but for commercial properties (likely broken down by office/retail/industrial sectors, and of course by region)? I can't find anything; I get the impression there must be something locked away behind paywalls at RICS or CBRE (who certainly seem to be able to put out plenty of commentary on short term price trends.)