Bigal1941
Is this not what Peter Dimmock refers to about 30 seconds in?
I know you say mid '50s and he mentioned 5 years previous.
Also see a memo by P. Dimmock on the subject of costs;
BBC - Archive - Aerial Journeys - Operation Pegasus Memo
BBC - Archive - Aerial Journeys - From an Aeroplane over London
The note at the end of page 4 is quite interesting !
Aaron