After serving in the First World War he spent much his working life in India and is regarded as one of the key players in the development of cricket in Madras.

[1] His battalion saw action at Second Ypres later in 1915, and Johnstone was wounded in the neck on 1 May, breaking two ribs and puncturing a lung.

A commission in the Regular Army followed and Johnstone was posted to the 17th Battalion, Lancashire Fusiliers at Arras in November, seeing action in the Somme in 1917.

After more recuperation he was passed fit for home service and took up a position as an instructor with the 6th Officer Cadet Battalion at Oxford for the remainder of the war.

[1] After resigning his Army commission in May 1919, Johnstone returned to Pembroke College, Cambridge, studying for a law degree.

[1][3][5][6][7] After graduating Johnstone was employed by a liquor manufacturer in Calcutta and then for a number of years by Burmah Shell in Madras as a manager.

[4] He was a member of the General Committee at Kent, particularly involved with the development of young players, and was President of the club in 1967, the year the county won the Gillette Cup for the first time.

[1][3][4] He died at his home at Eastry in Kent in June 1974, aged 78, after watching India play England in a Test match at Lord's.