The outfit is typical of the grey uniform used by many Rifle Volunteer Corps during the 1860s and early 1870s. The volunteer corps were similar to the militia, but were a different organisation (completely unpaid part-timers with a reputation at this period for amateurism).
From the fine detail, I am sure it is a real volunteer uniform. It could be being worn as a costume, but seeing the other post and the link to the full album, seems more likely to me the wearer was actually an officer in the volunteers. 'Dressing up' was one of the main attractions of volunteering, of course!