In 1979 Milton appeared in 3 hardcore stag films, in 2 he did not participate in the sex, in one he did. These films were never intended to be shown publicly, only at private "stag" parties, so Milton probably assumed they would never be seen, but when the British tabloids found out about his appearance in Arabian Nights (ironically not the one in which he performs), he became front page news and was blacklisted by the mainstream British film industry.
Arabian Nights (or Arabian Knights?) (1979) as
Servant. This is the one that caused the scandal. Milton might not be involved in the action, but he is inches away from it being a pervy voyeur. Strangely, for a film that was not supposed to be shown, this one has a publicity still of Milton in costume.
Schoolgirl Holiday (1979) as
Chauffeur. Milton only appears in the bits that pass for a storyline linking the "schoolgirls" various sexual encounters here.
Bustman's Holiday (1979) role uncertain. The only one where Milton does participate in the sexual action is, of course, the only one I've been unable to find. I did, however, find these sequenced shots from the film on an adult website taken from Super8, where you can clearly see Milton naked and joining in with the fun. Mary Millington's website says that this film has been restored in recent years, so hopefully I'll eventually be able to replace these images.