I’ve always wondered who the band in the early scenes of Antony Balch's Horror Hospital really were. Credited as 'Mystic' and with band members hiding out under some very suspect names (James IV Boris, Allan "The River" Hudson, Simon Lust), now it seems this mystery has been solved thanks to a response to this video on youtube which unmasks the band as late 60s British psychedelic group Tangerine Peel and the band members who appeared in the film as Warwick Rose (Bass), James Gaynor (Guitar) and John Warwick (Drums). The song "Mark of Death" was written by Rose under the pseudonym of Jason De Havilland (Rose appears to be the person who posted this info on youtube).
The cross-dressing frontman who appears in this scene, and gives Robin Askwith a bloody nose, wasn’t a real member of Tangerine Peel though, he was the film's co-writer Alan Watson, and seems to have been quite a wild character in real life. There are some great stories about him in Barry Miles' Burroughs biography 'El Hombre Invisible' “In Mason's Yard, behind Antony Balch's apartment in St James, workmen building the new Cavendish Hotel used to play football during their breaks. Alan would sashay past them, hand on hip, blowing kisses and squeaking 'Score a goal for me, boys!'". The workmen would howl with laughter and shout abuse, but Alan loved it. He was a real exhibitionist.”