Details of the accident from data on the mossie.org website
S/Ldr Arthur Jaques DFC & BAR was flying a Mosquito with the MAEE on 25/10/1945 on a practice `Highball` when the aircraft crashed in Machir Bay, Islay. With him was F/Lt Eric J.Saville, DFC. (Dave Earl on RAF Commands Forum) AB's 'UK Flight Testing Accidents' has this to say: 25 October 1945 Mosquito B.IV DZ579/G Sqd Ldr A Jaques DFC and Flt Lt Savin, MAEE, Helensburgh. Trials for operation 'Highball' flown from Port Ellen. Dropped a store at 30' into a rough sea. The splash caught the tail of the aircraft, the port wing broke off and the aircraft dived into the sea at Machin Bay, Islay (5546N, 0627W). 2 missing, presumed killed. Splash from drop test hit tall lost wing and dived into sea Machir Bay Islay 25.10.45 (Air Britain Serials)
Must admit I've not seen film of that accident. The more usual one to appear on the internet is of a Douglas A-26 Invader suffering a similar fate.