He can go and sort those pest 100% legaly,so what if there's lambs,pigletts or what ever outside the earth where the fox is.The law says "for the protection of game birds",well every bit of land in the UK has the right to dig foxes to protect the wild game birds as we all know there nesting right now and the law does not state in anyway what the land has to be like(forestry,heathland or hillside) nor does it state the game birds have to be released or reared.
Omegathelast your mate has every legal right to remove those pests,it's just IF he is ever asked why he is removing the pest he says it