It sounds like you might be right. It's either a woman or a man singing in a peculiarly high-pitched voice to harmonise with James Dean Bradfield. I've got the original Heavenly version of the song, though, and no-one is credited on the sleeve for backing vocals, so it might just be James or Nicky Wire. The only people mentioned who aren't in the band are Robin Evans (the producer & engineer) and Dave Eringa (assistant engineer, hammond & piano). Hope that's some help to you!