One way to find Moodles in use in FE and HE for the UK is by doing the following search on Google:
"Some courses may allow guest access" site:.ac.uk
It's not guaranteed to return every existing Moodle (e.g. they might be hidden from public access, in different languages or not yet indexed by Google) but as you can see there is a wide variety of usage in the sector.
Note that many places, particularly larger institutions, start with Moodle in a single department or faculty before moving to campus wide adoption. This potential for following a low-risk, measured roll-out approach is in fact a key benefit of Open Source, and therefore Moodle, adoption.
That's the model we followed at the University of Glasgow where Moodle was used by my department (GUIDE before being adopted as a centrally supported VLE. The size of our institution and its decentralized nature means we now have many independent yet interconnected Moodles, which you'll see if you follow the Google link given above.
I think it's important for people thinking about moving to Moodle to be public about it, as education organizations seem to have a bit of a herd mentality when it comes to IT adoption, which we may as well take advantage of. Given that Moodle has been in use in the sector for a while now, and is generally well received, combined with Open Source becoming 'respectable', even quite fashionable, in UK education circles in the last 12 months and that many multi-year license deals with proprietary alternatives are coming to an end, I could well imagine a mass-switchover to Moodle occurring. In fact I've already read two articles worrying that a Moodle monopoly would be as bad as a proprietary one. That's not an opinion I agree with, but it at least shows the mindshare that Moodle has.