The destroyer sent to intercept the SS Viking is the HMS Echo (H23). This was one of 9 E class destroyers of the Royal Navy. She was launched in 1934. During the Second World War she sank a U boat in 1943 and was transferred to the Greek Navy in 1944.
Several scenes were filmed at Brooklands - the Clubhouse and the banking are clearly visible. When the Ministry Dragon Rapide comes into land, a Wellington is just visible in the background. The test plane appears to be an Airspeed Oxford; other planes were Tiger Moths and Gypsy Moths, and possibly a Bristol Fighter (just the engine and propeller are seen).
This film was included in the first syndicated television presentation of a package of major studio feature films on USA television; it premiered in New York City Sunday 1 August 1948 on WPIX (Channel 11) and in Los Angeles Sunday 28 November 1948 on KTLA (Channel 5). The package consisted of 24 Alexander Korda productions originally released theatrically between 1933 and 1942.
The test plane was an Airspeed AS.6 Envoy (not the AS.10 Oxford - note the much larger rectangular windows behind the distinctive cockpit windscreen). First flown in 1934, it served primarily as a transport and training aircraft during WWII. Several variants were made, the primary difference being the engines used. One was outfitted for use by the Royal Family. Production ceased in 1939 with only 52 being made.