This Land Pattern bayonet is a private purchase weapon as there is no official Crown Inspectors Stamp, but it includes a "WG" makers mark.
Its a possibility that WG refers to William Grice & Son, Board of Ordnance contractor 176 c.1760-1782, 1789- 1790 *
The accompanying scabbard has its seam on the flat side so according to the Graham Priest** this dates it to after the order of 10th December 1784. As with figure 19 of this reference the offered bayonet locket is secured by a single rivet. The stitching is intact but the very tip of the chape is missing.
Our specimens locket no longer has the scallop and  brass stud attached which is likely due to a known weakness in the design.
Dimensions (mm): 
OL    BL    Socket    MRD    SM    BW
525    414    102    23.7    52.2    27.8
*British Board of Ordnance Small Arms Contractors, 1689- 1840, De Witt Bailey, Publishers WS Curtis, 1999. 
** The Brown Bess Bayonet 1720- 1860, Graham Priest, Tharston Press, 1986.