According to my line manager, if you get interviewed, there's a legal requirement to give feedback to unsuccessful candidates, at least if you've interviewed them. I replied that it be good practice and could be company policy, but I didn't think it was a legal requirement.
Not in the last 20 years certainly, and I would very much doubt if it was before that- there’s very little in terms of legal requirements around recruitment. Basically it’s don’t discriminate against anyone but otherwise do whatever you like.
The advice given by ACAS is probably a useful indicator. The only reference to feedback they make sounds like Good Practice based on the interviewed candidate's request, not a proactive statutory obligation on the part of the recruiting company:
Be prepared to give reasons for rejectionto unsuccessful candidates who ask