The full register, for each area, remains a public document and can be inspected, in person, at council offices.
Other than by personal inspection, current full registers are only available to authorised bodies, such as the police.
The national edited register is available online but most searches usually involve payment. (Check out www.192.com, www.theukelectoralroll.co.uk and www.eroll.co.uk).
The easiest way to search the national electoral roll is to use the UK-Info Disk. There are various versions of this product (with differing levels of search facilities). They're all expensive but most public libraries (of a reasonable size) have a copy (hopefully of the 'Professional' version) available for free consultation. (Libraries seem to have very different policies on these disks. Camden library service told me that they they don't have these disks because they breach Data Protection legislation [which is utter rubbish]. Suffolk library service, onthe other hand, were happy to spend nearly an hour locating the relevant software so that I could view the last publicly available version of the full register).
Forget the internet. Head to your local library - unless, of course, you happen to live in Camden!
Chris