What we need is a good closeup of just the 2 cap badges, from this we should be able to identify the Regiments.
Also the civvy at the back appears to have what may be the SWB so a closeup of his lapels too. If it is the SWB 1916-18.
The Silver War Badge ( or the silver wound badge as the men referred to it ) was awarded to men who through injury or illness were rendered unfit for further active service. First awarded Jan 1916 but became surplus to requirements by the end of the war & finally discontinued 1922.
Something about the men.
The soldier on the left looks like m/c gun Corps. He is a L/Corporal & has one good conduct stripe.
The soldier on the right can't be identified as to Regt. but he has 3 good conduct stripes & 1 overseas stripe which was first awarded in 1917.
A good conduct stripe was awarded after 2 years of service, 3 after 12 so the one on the right is a career soldier of at least 12 years.
So a confirmed date of 1917-18 in lieu of it being the SWB .