The aircraft used in the movie were the Hawker Siddley T1 Gnat
two seat advanced trainer. Derived from the single seat fighter the
Folland Gnat, the TI version was extensively used the Royal Air
Force as an advance trainer replacing the Vampire.
Most used by 4FTS RAF Valley, Anglesey in the sixties and
seventies until replaced by the BAC Hawk. The T1 was also flown
very successfully by the RAF's aerobatic team The Red Arrows based
out of Little Rissington.