Following the death of a local lad in my daughters year at school following a tragic air rifle accident, I was discussing the law with a police mate of mine. He pointed out something that I had no idea about and I doubt many others have either! The Violent Crime Reduction Act 2006 made some changes to how air weapons may be sold. It would appear that private sales of air rifles between individuals where neither is a registered dealer is illegal!
See section 31 & 32 here: