Lets be sensible, he's selling it to an airsofter for the purpose of airsoft. I was operating on that assumption because that's going to be the case 99.5% of the time, to assume otherwise is an unnecessary obfuscation of an evident truth.
If that which you have quoted is intended to be the part which related to airsoft, then well, ya know, bang me backwards and call me shirly, you lot need to get rid of your law-makers before they make anything else so vague. I thought the purpose of legalese was to make it so something had no wiggle room, but you could drive a train through that hole.... But that was my initial point anyway, he doesn't really need a valid defence in the normal sense of the word (IE: an active UKARA number ) in this scenario becasue he already has one so long as the person to whom he is tranferring the gun has valid defence.