First the good news . The mark is almost certainly that of Joseph Fletcher (Grimwade page 393 under bucklesmakers) He entered two marks as bucklemaker in 1781 and 1783 but other than the addresses given by Grimwade have no further information on him. I've not seen his work elsewhere and this is the first indication that he was still marking buckles in 1798.
Now the bad news .
I'm afraid I think this is a pair of Georgian Shoe Buckles altered around 1900 to a girdle clasp .
I had a suspicion this was the case when I noticed the irregular wear to the sides not making sense , but it's been done so well I was not sure
This buckle looked Georgian, had Georgian marks but was a new form. It certainly got me very excited indeed initially until I noticed the wear anomaly
Cuts made were as shown below to the original buckle frames
The small piece was then reversed and welded internally to the larger outer piece and later clasp bars added
I had seen this done once before but never as well as this . I’m virtually certain this is late Victorian Edwardian recycling of an obsolete item and never intended as a fake in any way - but I'm not sure how Goldsmiths Hall would view it . I do not think it comes under the heading of substantial alteration to the nature of the piece as its still a buckle !