I'm finally getting around to cataloging/labeling some photos and I was wondering if anyone here could point me to a resource/s online(?)that would tell me which British regiment(s) were on public duty (guard duty) in the London area a couple of years back.

Nothing nefarious in mind. I just want to put the appropriate captions to these photos. (Like "Member of the 8th Light Infantry on duty at Windsor.")

The guards on duty at the time weren't the standard foot guards regiments (Grenadiers, Coldstream, Scots, Irish and Welsh) with the scarlet tunics and bearskins that everyone's familiar with. They were wearing black or dark blue tunics, trousers with red stripes, and the peaked cap (visor cap or service cap to the US vets) of the regular army.

I can provide specific dates & locations if you don't want to share your resource(s). I'd even be willing to share a couple of the photos if it would help. I think I've got a pretty good idea for at least one day, but I'd like to confirm it.

Thanks in advance.