The photograph appears to be taken at Fenham Barracks Newcastle which was the home of the Northumberland Fusiliers . The steel helmets are MK1`s (displaying unusual paint camoflauge) The MK III helmets were the ones issued shortly before D-Day.
The `White` uniforms are not tropical issue but `Fatigue` or work uniforms Shirts; Fatigue smocks & trousers made of unbleached canvas and later denim supplemented with Jerseys/Cardigans. The Khaki Tunics are british service dress 1922-39 (although due to shortages after Dunkirk old stocks were re-issued.
Fatigue dress had long existed with the more formal `smart` uniforms saved from staining and wear by the introduction of these items . After 1939 it was generally replaced by “Denim Overalls”. Between the World Wars use of shirtsleeve order and of jerseys had greatly increased in the tropics and from World War 2 onwards this spread to temperate regions. New informal/working forms of dress multiplied apart from coveralls etc. these consisted of combinations of various shirts, jerseys, trousers and headgear .
In June 1935 George V celebrated his silver jubilee. This opportunity was taken of granting royal status to four regiments, principally in recognition of their service in the previous war the Northumberland Fusiliers were one of them becoming THE ROYAL NORTHUMBERLAND FUSILIERS . In 1936 they were one of four infantry regiments selected to become `Machine Gun` Regiments.
On September 17th 1936 the 1st RNF sailed for Palestine and were still in the desert at the outbreak of WW2. 2nd RNF were the first British Regt in France on 1st October 1939.
Just for information clarification .
Jim
