Flook only has 4 lines about your style of knife. He says there were marked and unmarked versions. The marked version had the Air Ministry stamp, which would be a Crown over AM. He also says the marked one has a maker's mark of G.I & Co. which would be George Ibberson and company. Ibberson made a lot of knives for the British military. The folded single piece body being typical of a couple models of Ibberson knives.
The Made in England stamp on yours makes me think post-war production or at least post-war sale. From 1930 on, items imported into the US were required to be marked with the country of origin. Stuff in the 50's and 60's was often marked with Made in XXX. Since the 80's or maybe a bit earlier it seems like markings have changed to just the name of the country. Great Britain was in a world of financial hurt after the war. We don't think about it in the US but rationing in the UK went on until the late 50's. The cutlery industry, like all the businesses that had geared up for war production were hurting for work once the military contracts were cancelled. Ibberson was one of the better known knife makers. From the mid 1800's until 1980 it was a family owned firm. Bought by a bigger fish, the Ibberson trademark is still in use on knives.
It would made sense that if they had left over production from military contracts they would just stamp the Made in England on it and bingo, instant export product. It is not uncommon to find the British WWII issue folder with no military markings indicating either post-war production or more likely leftover military contract production sold off as commercial product.