Early St John’s Ambulance, Red Cross & Girl Guides were quickly eliminated leaving me to conclude the uniform could be an early version of that worn by a forerunner of the Church Girls Brigade or similar organisation; the “white sash” has a pouch just below the belt.
As the picture was taken in England it could be the Girls Life Brigade founded by the National Sunday School Union in 1902, modelled on the Girls Brigade,Ireland (f 1893) and the Girls Guidry,Scotland (f 1900).
I’ve not been able to locate an image that is the exact same but if you google for – girls life brigade 1900 – although the dress is different you should see the Slouch style hat features in the uniform shown in an illustration of “early girls life brigade” but no date.
If you click on the image you should be taken to a page describing Civilian Uniforms, scroll down to Youth Organisations (3/4 down the page, you will see just above the image it describes the early boys uniform of the 1920’s &1930’s, but it’s obvious some text is missing when it ends with, “The remainder of the uniform would be a dark blue skirt, white blouse and (for some) a blue jacket.” So it’s certainly possible the earlier version could be like in the picture.
To get confirmation I can only suggest you contact the Church Lads’ & Church Girls’ Brigade Archivist Robin Bolton see http://www.nationalarchives.gov.uk/archon/searches/locresult...