Thanks for your comments. As to the booklet’s originality that raises some interesting points. I am 100% sure it is authentic because I know I have certainly had it for more than 30 years, and back then colour digital printing was unheard of. Also, the cover is embossed in gold, something that would have been very difficult to emulate. Finally, I gave it the ultraviolet test, using another Webley booklet which is definitely a reproduction for comparison. This picture https://imgur.com/a/CGYRV shows the two booklets under normal light , and this picture https://imgur.com/a/Ronca shows them under uv light. The blue fluorescence from the reproduction proves it was printed after about 1955, whereas the complete absence of blue from the authentic one is consistent with it being printed on pre-1955 paper.

Given the authenticity of the booklet and its good condition I think that upper estimate of £20 would be more likely. Perhaps, as it is obviously much rarer than a green or orange Webley pellet tin which regularly fetch about £20, it might be worth a bit more to someone who collects Webley literature?