AGS seems to have been a pupil at Dulwich College: https://www.familyre...Dulwich College
I've also found a further reference to what may be our man in the London Gazette, 21 May 1943, Issue 36024, Page 2273. A Sgt Alan Gascoigne Sinclair is one of a large number of NCOs who were granted an emergency commission as 2nd Lieutenants. In the Indian Army. Rank effective 12 December 1942. Unfortunately no service numbers are quoted, but is this our man? Is he one and the same as the RN reserve officer, whose seniority dated from a couple of months later in the Royal Indian Navy?
And another of AGS's exploits in Australia ...
RACE DRIVER AND
GIRL INJURED
Collision With Trolley
ADELAIDE, Monday.-Alan Gascoigne
Sinclair, aged 31 years, of Hewitt avenue,
Rose Park, engineer, who came to Aus-
tralia a few months ago to take part
in the Grand Prix motor races at Lobe-
thal to-day, was slightly injured when a
car which he was driving collided with
a horse-drawn trolley at the intersection
of Ackland and Flinders streets.
A girl cyclist. Margaret Murley, aged
18 years, of Ackland street, was also in-
volved in the collision, and was admitted
to the Adelaide Hospital suffering
concussion, lacerations, and a probable
fracture of the skull
Sinclair was also taken to hospital, but
was allowed to go home after treatment
for a lacerated scalp.
The Argus (Melbourne, Vic.) Tue 8 Mar 1938 Page 3