Yep, I agree with Martyn. The leather jerkin was actually an item of clothing dating back to the First World War, but was just as popular in WW2. It was frequently worn by "technical troops" such as machine gunners, as the lined jerkin gave extra padding when humping the heavy gun parts around. "The World War II Tommy" by Martin Brayley and Richard Ingram,a full colour photograph book of reconstructed British uniforms, contains a five page section covering a Vickers crew, and depicts both wear of the jerkin and the machine gunner's proficiency badge as depicted in the set, as well as an assortment of ammo boxes. Note also that as well as the cover on the barrels, one is depicted with the prominent flash suppressor, which was a later war modification and one without. Classed as a Medium machine gun, the Vickers was supplied to the machine gun platoon in infantry battalions (6 guns), as well as Medium Machine Gun Battalions in Infantry Divisions. In both World Wars, the Manchester Regiment and Middlesex Regiment provided MMG Battalions.
The bandoliers were of a cotton fabric and were intended to be folded up into the ammo pouches. Infantrymen would acquire as much ammo as they could, so when the pouches were full (60 rounds) extra ammo could be festooned in the bandoliers.
"Lord Raglan wishes the cavalry to advance rapidly to the front, follow the enemy, and try to prevent the enemy carrying away the guns. Troops of Horse Artillery may accompany. French cavalry is on your left. Immediate. Airey."