Hi Olga! For a UK English alternative, really just because I like the words, I suggest "sponger" or "parasite" too.

Hey Chris! :) Yeah, I've thought about "sponger" too, but it has a slightly different meaning than "нахлебник" in Russian. Нахлебник usually is a relative (or a person close to your family) who lives with you under the same roof and takes advantage of your hospitality. Parasite is a good term too.