This is a very nice example of the "straight grip" Mk1. This model was made between 1924 and 1935. The Mk1 models which came after this one had more slanted grips which were made from Bakelite. From the Serial Number it was probably made around 1931. Value in my opinion will be around £200, but we don't see many nice Mk1 pistols for sale on this forum. Other Webley collectors will no doubt have their own ideas.