Hi Lynn,
Burton-upon-Trent is actually in Staffordshire, and is therefore not covered by my web site. However, I'd be happy to have a look at your photograph and estimate a date for it. I have seen various George Renwick photos before - in fact, I have a carte de visite of my gg-aunt Sarah Payne nee Parker (1870-1946) taken in the late 1880s, when she was probably in service nearby.
Mike Harbach's GENUKI Staffordshire Photographers' Index shows George Renwick to have been operating a studio at 20 Station Street, Burton in 1880, 1896 and 1900, after which he moved to 4 Bank Square by 1912.
If you would like to send me detailed full colour scans (at 300 dpi) of both the front and reverse of the photo, including the full extent of the mount, saved as JPG files, I can probably narrow down the date at least to within 3 or 4 years.
By the way, Prue, the Renwick photo on your Victorian Photos (Rootschat) site I would estimate was taken in the early 1880s.
Regards and best wishes,
Brett Payne
Tauranga, New Zealand