Agree - VERY memorable indeed - saw it on both transmissions including the first time in 1974 and the Valentine special. Julia Foster was an understated glamour girl of the 1960s who was also in 'Half A Sixpence' - also played 'Gilda' in Alfie. There were many TV one-offs around this time but this leaves a lasting impression - you almost hold your breath and it stays with you too.
About time this was available on DVD or shown again. A real gem that just sits in storage somewhere. Last I saw of Julia was in a TV ad with Michael Winner (she was the one to whom he says "Calm down dear" - uncredited) If this ever appears on television again - DO NOT MISS IT!