David Hemmings had clearly forgotten the climax to this film because in his autobiography he describes a totally different ending to the film. (This book is very clearly ghost-written and did not appear until Hemmings had been dead for a year - it seems likely that the actor himself had very little actual input into it).
Homaged in Endeavour S5/6 Icarus [11/3/18]
This was originally a play for radio by Giles Cooper, who adapted it for television in 1962.
Very similar in plot and storyline to Sidney Lumet's " Child's Play" which was released the following year.
David MacGill (now 67) had a speaking part in this movie which was later cut due to creative differences with the director.