This is a Significant Record milestone.
The record of 200.07 kph/124.2 mph was established in the piston engine class for speed over a 3km course. The course followed the railway line adjoining White Waltham airfield. See FAI record # 13128.
The pilot was Squadron Leader Henry "Basil" Arkell.
Source: “A History of British Rotorcraft 1866-1965”, Compiled by R.A.C. Brie, August 1968, Westland Helicopters Limited, Page 125