Later in the war, he served in the Royal Naval Air Service in the Eastern Mediterranean before returning to Great Britain where he worked to organise the Machine Gun Corps and manpower planning.

After the war, Sykes was appointed the Controller of Civil Aviation and he continued in this role until 1922 when he entered politics, becoming the Conservative MP for Sheffield Hallam, which he held until 1928 when he resigned.

[1] Following civilian employment as a clerk and after working on a tea plantation in Ceylon,[1] Sykes enlisted as a trooper in the Imperial Yeomanry Scouts regiment of the British Army at the start of the Second Boer War.

[9] As a firm believer in the importance of wartime aerial reconnaissance, he was chosen to join the sub-committee of the Committee of Imperial Defence which was given the task of investigating the use of aircraft.

[12] On 9 July 1913 his role was restyled as Commandant of the Military Wing of the Royal Flying Corps and he was granted the temporary rank of lieutenant-colonel.

[10] Although the configuration and effectiveness of the deployed forces owed much to Sykes, as a middle-ranking officer he lacked the seniority thought necessary for command in the field.

On 21 December 1914, Henderson resumed command of the Royal Flying Corps in the Field and Sykes was granted the temporary rank of colonel and once again made his chief of staff.

While Churchill was preoccupied with implementing post-War defence cuts and the demobilization of the Army, Sykes submitted a paper with what were at the time unrealistic proposals for a large air force of the future.

[29] Being dissatisfied with Sykes's performance, Churchill decided to reinstate Sir Hugh Trenchard, the previous Chief of the Air Staff.

[30] Accordingly, on 1 January 1919 Sykes was appointed a Knight Commander of the Order of the Bath[31] and allowed to take early retirement with the rank of major general with effect from 31 March 1919.

[32] Sykes was appointed a Commander of the Belgian Order of Leopold on 15 July 1919[33] and awarded the American Distinguished Service Medal on the same date.

[46] Sykes returned to Great Britain in 1933 and for the next six years he held various directorships and official committee posts including with the Miners' Welfare Commission and the British Sailors' Society.

After the death in May 1940 of Terence O'Connor, the Solicitor General and MP for Nottingham Central, Sykes was returned unopposed in the resulting by-election.

[53] Geoffrey de Havilland wrote to Isabel after the cremation: "I was deeply touched by your husband's wish that I should scatter the ashes over Salisbury Plain.