Source: Joined battalion per War Diary entry June 20, 1916.
Duty Nobly Done describes an action in which Lieutenant Sykes was involved:
In the interlude between the two stages of the barrage, the Germans attempted a spoiling attach on the positions of the 18th and 20th Battalions. A few of them managed to reach the jumping off trench before Lieutenant Hugh Sykes and some of the 18th Battalion men with help from Lieutenant Gidley and some bombers of the 19th, in support of the two forward battalions, drove them off. In one case, Private David Egan picked up a Lewis gun and moved out of the trench [during the September 15, 1916 attack at the Somme] to a position from which he could enfilade the attacking Germans, causing many casualties among them and forcing the survivors to withdraw.
Antal, S., & Shackleton, K. (2006). Courcelette: Taking a Turn On the Somme. In Duty nobly done: The official history of the Essex and Kent Scottish Regiment (1st ed., p. 211). Windsor, ON: Walkerville Pub.
For conspicuous gallantry in action. He held a section of trench and repelled an enemy bombing attack with great courage and determination. Later he gallantly led his platoon forward, and captured an enemy trench. He was severely wounded.
The London Gazette
Publication date: 14 November 1916
Supplement: 29824 Page: 11081
rom the Annals of UTS Schools, 1914-1916 – “Old Boys Decorated for Valor”:
LIEUT. HUGH H. SYKES
Hugh Harding Sykes was educated at the University Schools. He qualified for a commission and was appointed to a lieutenancy in the 35th Battalion. Early in the spring of 1916 he was transferred to the 18th Battalion and went to the Ypres salient in June. Later the division was moved to the Somme where he was severely wounded on September 15th. 
For gallantry on the field he was awarded the Military Cross, the investiture taking place at Buckingham Palace on November 3. 
Lt. Hugh H. Sykes’ name appears on the bronze memorial plaques located in the lobby of UTS Schools, Toronto, Ont.
His portrait appears in the Annals booklet1.
1M. I. Pirie, Private Collection.