I think there were really supreme satnic HM bands during 80's a clear inspiratio for Black Metal I think!
I can say that some NWOBHM acts had really satanic direction like Angelwitch, Demon, Cloven Hoof(their debut is one of more haunted records around), Satan,Satanic Rites,Demon Pact(similar with Venom and they were formed in the same period), Witchfinder General,Witchfynde etc
Also latter existed bands like Coven(USA), Satan's Host, Crush(Gre),Ritual(Bel) with very evil feeling and aura.
Some other old bands hailed from other countries during late 70's early 80's too like Future Tense or Death SS
Finally I think there existed some other bands that was a huge inspiration for Black Metal only music wise like Cirith Ungol,Manilla Road or Warfare