If you know the name of the person and maybe even some people that they live with?
You can try the website www.192.com and do a name search across the uk for everyone with the same name. It can also give you the names of other people they live with so that it helps make you match who you are looking for. To do this it uses all of the UK electoral roll records and phone records. If you think you have found the match then it will give you an address even if not a phone number. You do need to sign up and buy credits to be able to do a search that shows the addresses