I'm a member of this one (as I live in mainland Europe)
http://www.scdb.info/my/index.php
Al...

to that - I use it too. If you're only interested in one solely for the UK then there's one at
PocketGPSWorld that also includes favourite locations for mobile units (the scdbinfo one does not include mobile locations) but it is more expensive.
Whichever source of data you use, you will need to get a copy of
Garmin's POI Loader to be able to load it to your SP2820 as Custom POI's. If you download and install the POI loader and then read the help topics that come with it you should get the gist of how it works. The key thing is that you have to have all the POI's you wish to load in the same folder on your PC, and the loading process is not additive as far as your SP2820 is concerned, i.e. whatever custom POI's are on the device get erased before the "new" POI's are loaded.
A second point is that when loading proximity/speed warning POI's all the data must be in the same units (i.e. mph and feet
or km/h and metres). If you use the scdbinfo data then the UK data is supplied in mph while the continental europe data is supplied in km/h so you have to convert either the UK filenames to their km/h equivalent or the other way around.
Post back if you need more help...