Just a guess
I suspect that the "DE GG" are the owner's initials and not the maker's marks. I checked my copy of Blackmore's Gunmakers of London and Gunmakers of London Supplement and did not see any maker whose marks are similar. Richard Wilson made a similar gun but it did not feature a folding trigger (see Howard Blackmore's, English Pistols, page 15). J. N. George has several pocket pistols (or muff pistols if you will) illustrated that are similar on page 99 of his book, English Pistols and Revolvers.
Try contacting a curator at the Royal Armoury in Leeds or the Frazier Historical Museum in Louisville, KY.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!