Looks like a flintlock single shot .....maybe french because of the trigger design and the plate....hard to tell from your photos. Is it an octagon barrel....cant tell from pic. But as soon as the gun experts here see it they will be able to tell you.
I go a great distance,while some are considering whether they will start today or tomorrow
Gypsy, the hammer appears to be more of a percussion style thus putting it more in the mid 1800's.
I'm thinking something along the lines of either:
A good 50 bore percussion pocket pistol by D.Egg, London, with some original finish, Birmingham proof marks, circa. 1840.
or
A very good 60 bore percussion pocket pistol by Burrows & Son, Preston, Lancashire, retaining nearly all its original finish, 7" overall, Birmingham proof marks, circa 1840.
It's difficult to tell from the pic although it could also possibly be a variation of the Philedelphia derringer. If so, some of the sideplate is missing. Is the hammer on the left or right side? Although most were hex barrels, the one linked bleow isn't.