Its an unlicensed copy of the Webley RIC (Royal Irish Constabulary) model, circa 1870. As one of the most popular weapons in Europe at that time, the RIC was copied by numerous British and Belgian gunsmiths with quality varying from abominable to quite good. Yours appears to be one of the latter.
Unfortunately, the mists of time have washed away all record of many of those gunmakers and you may never know who exactly built it. Google-fu is your best bet, but don't hold your breath.
Caliber is likely .38S&W or .38 Tranter Rimfire, but there were all kinds of weird cartridges running around Europe back then, and I wouldn't try to fire it without at least slugging the bore.
Perhaps Mike Tinker-Pearce will chime in on this, I think he's a bit of a guru on the RIC.
Thanks for sharing, and welcome to the forum!