An official photo describing the kit of a British infantryman in 1939. Note that the gas mask ('respirator') and anti-chemical warfare cape are parts of the outfit, remnants of WW1 memories. In actual combat, and marching with full kit, the British infantryman would carry a pack known as a "valise" that contained more clothing and personal items. Officers wore the exact same uniform save for markings of their rank.
July 1, 1916. The First Day of the Battle of the Somme. Despite the heavy loss of life and failure to achieve the expected breakthrough, Field Marshal Haig and General Rawlinson deemed the attack a success, so much that the offensive was to continue for a further four months, only ending with the onset of winter. - prisonersofeternity.co.uk