'Sim's biographer comes to no firm conclusion - although he defends the actor against any innuendo about his sexuality by saying: 'Suspicion is the new social currency.'Nevertheless, he makes clear that Sim - while often notably generous and tender-hearted - could be a manipulative and difficult man, with 'limited acting ability'.
So let us try to unravel the truth about the actor who starred in the first Ealing comedy, Hue And Cry, in 1947, appeared in Alfred Hitchcock's thriller Stage Fright in 1950, and the film version of J. Priestley's An Inspector Calls in 1954 - and whose performances inspired Alec Guinness.
'From that day, and for the next 50 years, I had need to look for no one.' At her 13th birthday party, just a few weeks later, Sim kissed the new teenager, and she remembered afterwards: 'I had difficulty getting to sleep that night.' The actor also took care to befriend his new admirer's mother Norah - launching a relationship that was to last 'for many years'.
Sim became an ever-present guest at the Plaskitt's flat in Edinburgh and took an 'increasing interest' in his devoted admirer's education - to the extent of suggesting that Naomi leave school at 14 to enrol as a pupil in his drama school.
Sim's closeness to the young actor 'drew comments from some quarters about the appropriateness of the relationship', says Sim's biographer.
'Even suspicion from some that it was not entirely healthy'.
But the actor's friends dismissed this as 'nonsense'.
Cole, who is now 83, merely describes his mentor as 'deeply caring'; while the TV producer and director John Howard Davies - who appeared as Oliver Twist in David Lean's famous film - suggests that Sim simply 'wore his heart on his sleeve' which made him 'vulnerable to all sorts of allegations'.
What his friends may have seen as 'no more than innocent kindness' towards the impressionable boys and girls with whom he surrounded himself could well have been misinterpreted - and destroyed him.But that facade may have concealed a darker truth for, as a new biography of the actor reveals, throughout his life, Sim carefully cultivated 'friendships' with teenage boys and girls as young as 12.And the Edinburgh-born Sim did everything in his power to keep those proclivities private - refusing countless interviewrequests throughout his career, and declining to appear on radio or TV chat shows.'All the public need to know about me is what they see,' he insisted.A few months later, he was asked to play the part of a priest in an amateur production of the play The Land Of Heart's Desire, and was introduced to one of his co-stars, a 12-year-old girl who 'looked much younger than her age'.The younger of two sisters, Naomi Plaskitt was swept off her feet when she met Sim.'He was tall and gangly with crisp black hair already receding, a lively face with huge eyes and a very beautiful smile,' she wrote later.With his bald head, pouchy deep-set eyes and lugubrious face, Alastair Sim was one of the film legends of the Fifties, the star of Scrooge as well as the first, and best, St Trinian's comedy - in which he played not only the school's headmistress, but also her scheming brother.