Discogs is my preferred source for both new and out of print, used discs. I’ve had bad luck with dishonestly/carelessly graded used cds on Amazon marketplace. Ebay is somewhat better but in my experience, Discogs is the most reliable and allows you to search for a specific edition of a given release. So if you want a MoFi hybrid SACD ,Japanese UHQ or West German edition of a given title, they’re all listed under the title, along with the US domestic versions.
It may be that Presto has a wider selection of new Classical disc’s. I can’t say. Otherwise, I can't see the advantage or ordering from the UK.