Personally, I wouldn't like to see anymore laws brought in for airguns - I think the ones that we have are sufficient as long as the full weight of them are used against those that do wrong.
I know of someone that uses an air pistol to finish off trapped squirrels if need be but, this is at point blank range.
Air pistols are great fun for targets but, I certainly couldn't condone hunting with one. I do feel for you chaps in the industry that have to deal with some of these enquiries.
To be honest, by trying to educate people and, sometimes refusing the sale, I don't see how you can do any more.
Also, I thought there was already a law about causing unnecessary suffering by using the wrong tool for the job and/or taking silly, chancey shots? (I'm happy to be corrected)
The trouble is, who's going to know what some of those dipsticks get up to on their permissions.