ALTHOUGH the singer himself confessed to Keeping Posted that he didn't know what kept him so long, Peter Gabriel - the socio-musical conscience of the world - seemed well-pleased that at last he has got to this part of the world. And with quite a few Steve Bikos languishing in jails across the mainland, there's enough material over there for a complete Gabriel album. Incidentally, during our quiet supper-time chat, Gabriel pointed out that he lives near Bath, the former constituency of Chris Patten. He said: ''When Patten was the Member of Parliament there I lived just three miles from Bath and in fact met him once at my daughter's school.'' Then, in a forthright endorsement of all things Pattenesque Gabriel extolled: ''I have never been a supporter of the Conservative Party, but right now I strongly believe that Patten is the best man among the Tories to be prime minister.'' So there.