In this interview, voice actor Marc Silk states that he appeared on the BBC's Radio 1 Breakfast as Shaggy and Scooby-Doo in 1998 when Zoe Ball was hosting the show. Silk states this appearance had something to do with the merger between Hanna-Barbera and Warner Bros. Animation that was going on at the time. He doesn't make it clear if this appearance was sponsored by Warner Bros., but given the fact that Silk later voiced the duo in later UK promo material, it's not an impossibility. From my searching, I'm unable to find this broadcast but maybe I'm just not looking in the right places.