Even before Al Stewart went to California he was not your traditional folk singer type, though he played a lot of folk clubs in the UK in a period in the late 60s as that was a big circuit and a good arena for a single acoustic singer-songwriter to get going. His subject matter was often very intropectively personal (and sexual) or intriguingly but kind of academically historical. I doubt he often, if ever, played a traditional song or instrument, and he wasn't engaged in current-affairs protest-type songs in the 60s either, or songs of work and industry.
He started his career in a band with Tony Blackburn, of all people, and his first album was orchestrated and premiered in a concert at the Royal Festival Hall with an orchestra. In later years he produced a kind of folky-pop-rock, and even on his early albums his session musicians included the likes of Jimmy Page and Rick Wakeman. The only time I saw him was in Manchester with a rockish band in about 1978, I guess.
My personal album favourites are Bedsitter Images, Zero She Flies and Past, Present and Future, though I like quite a bit from other albums as well, especially the early ones.