I have just received some info from a good friend who is quite an expert on uniforms and indentification, this is what he told me.
They are wearing 1902 pattern service dress (SD), but the slouch hat was officially prescribed that year as the field head wear to be used with SD (at home as well as overseas), so I would date the photo to that year. Interestingly all the men are wearing Slade Wallace pattern waist belts from the 1888 equipment, but some of them have leather bandoliers, which as this seems to be prior to 1903 and missing the later matching leather waist belt, must be of the 1897 pattern.
One note of caution though, neither the men nor the officer appear to be wearing spurs (as far as I can see?) and they are armed with either Lee Metford or Lee Enfield Rifles. It seems possible then that they are not yeomanry, but a TF battalion of the Cheshire Regiment, and the men with bandoliers are perhaps the mounted infantry section that each TF battalion was required to have at that time. Examination through a glass of the officers slouch hat badge might help to confirm an ID
So it seems they are not Yeomanry but a Territorial Force.
I am very gratefull to him for sharing his knowledge.
Paul