I thought it was a sensitive, enlightening, serious and amusing delight pushing the boundaries of conventional attitudes and prohibitions about desire.
Nancy reflected the culture conveyed to well brought up girls in the fifties at least outside London. Passive acceptance of virtue and chastity until sanctioned by love and marriage. Sexual thoughts or activities were " bad" or impure but OK for the male of the species.
Unlike Frank Kermode, I found the character of Leo credible. His preoccupation with his mirror image reflected the insecurity of the child who has not been mirrored in the eyes of his mother. (Winnicott) as the beloved prior to the later downright and absolute rejection. If one relies on the psychoanalytic theory of Fairbairn, deprivation and frustration may lead to eroticisation. Gratification can be found in being the object of desire of the other. The internalisation of the real mother's rage is manifested in his response to Nancy's attempt to access his non professional life but later she gives him her acceptance and "well done". The film then gives the impression of real life attraction when he responds to the young waitress.