This may have come up before, but I can’t find anything with a quick search.
CAMRA has a wealth of info on pubs, often that they have closed + new use: eg, https://camra.org.uk/pubs/samuel-pepys-slipton-160630
I don’t think we can use this info directly. Is it worth getting their permission to incorporate their data (as a reference point, not as an import)?
If so, does anyone have any contacts there to tap up first?
Somewhat related, a while ago I got permission to use data from the lost pubs project (https://www.closedpubs.co.uk/) for OSM mapping:
File:Lostpubsproject-permission.pdf - OpenStreetMap Wiki which might be useful!
CAMRA’s information is of course volunteer-collected just like ours. There’s also a fair bit of overlap between the people doing the updating 
I’m sure that there are plenty of pubs that CAMRA has recorded as shut that OSM still has open, particularly in areas where there are relatively few OSM mappers, but I’m not sure what you’d do with “someone thinks this is shut now” beyond e.g. leaving a note? An OSMer is still going to need to check the on the ground situation to update OSM.
Depending on where you are in the country CAMRA data may be updated almost instantaneously after a real-world change, or be a few years out of date. Sometimes the rate of change is so fast that it’s understandable that updates (in OSM or elsewhere) will lag behind reality, even in areas that are updated pretty quickly. See also here.
I was assuming that the ground check by CAMRA volunteers would be good enough for OSM: it seems a well organised project, and cares about the quality of its data.
In my particular cases, there was info already on OSM that could be augmented or corroborated by CAMRA: Note: 4717383 | OpenStreetMap and Note: 4636165 | OpenStreetMap
But if the consensus is that OSMers must verify CAMRA data on the ground, then you’re right that it’s not much help beyond “there’s something to check here”.
For that second note that originally asked for opening hours, those are hard enough to collect for CAMRA’s pub database (I am co-ordinator for our local branches pubs - some have the times on chalkboards and update them frequently). I doubt you’d get CAMRA to share their national dataset, but I try and keep my branch area’s pubs updated (though sometimes miss a change and surprise myself when I spot a pub in OSM with an old name or whatever).
If not their whole database, the “pub closed, remove from maps” fields would be grand!
PS and ofc if they can also say “this one’s now a mosque” I would be especially delighted