Hide and Seek (1964 film) - Wikipedia

1hr 30mins
Dir: Cy Endfield
Starring: Ian Carmichael and Janet Munro

A reserved British astronomer is drawn out of his quiet life and into an affair of international espionage

There are some good shots at Watford Junction in this thriller, taken on the now disused former platform 12. There is plenty of maroon coaching stock present, but no locomotives. However, the train journey which follows is depicted with the stock shot of un-rebuilt LMS ‘Royal Scot’ Class 6P 4-6-0 No.46100 Royal Scot complete with ‘THE ROYAL SCOT’ headboard on Bushey troughs. This shot also features in the following productions; Cage of Gold (1950), Escapade (1955), Left, Right and Centre (1959), and Beat Girl (1960) (all qv). Its origin is not known, but by 1964 it was a bit long in the tooth.

Ian Carmichael on the old platform 12 at Watford Junction
Looking the opposite way (south towards London) and a train is visible in the background
A brief moment later and a train arrives but we do not see the locomotive. The platform here is still extant today but trackless.
The now familiar and much-used stock shot of Royal Scot on Bushey troughs which is at least very close to Watford Junction