So far, I reckon that about 10% of shops in the UK have been added to OSM, but it's a bit of a mixed picture.
The coverage varies by type of shop. Post Offices and Cycle shops seem to be well covered (I reckon that about half of each are in the database). Garden Centres, Clothes shops and Computer shops are covered better than most types of shop (around 20% of each have been included). Butchers and Off-licences are close to the average (at around 10%). However I can only find a small proportion of the expected number of Flower shops, Furniture shops, Fishmongers, Greengrocers and Hardware shops. On face value the coverage of supermarkets is particularly good, but these are difficult to classify accurately so these figures are a bit iffy. Given the public spirit that drives a lot of OSM activity I was slightly surprised to see that coverage of charity shops is quite low (6% or so).
There are regional variations. I reckon the most densely mapped areas have recorded around half of the shops on the high street, while the less well covered have recorded only one shop in a hundred. These rankings for shops follow a different pattern to the rankings of road coverage. For example, Derby and Islington are doing particularly well recording shops. Although Islington also comes fairly close to 100% in the ITO comparison with Ordnance Survey road data, Derby comes further down the same rankings. Wolverhampton does pretty well on both rankings, while Wigan scores well on streets, but near the middle on shops.
(with apologies to various rural counties, there was an error in the previous version of this map, which this one seems to fix)
To produce the map I extracted OSM data related to shops, and allocated each within the relevant local authority boundary. For comparison I use National Statistics on the distribution of retail units by local authority. This only covers VAT and PAYE registered businesses, so it will understate the actual numbers of shop units in each authority. Hence the raw percentages will be over-stated. However, it should be a good enough proxy to compare geographic distributions. To measure the proportion of each different type of shop recorded in OSM I used estimates of the actual number based on a mix of public domain data from National Statistics, Valuation Office data drawn from business rates, and figures from various trade bodies, and industry analysts.