Nic and Jan-Marie
Many thanks for your very comprehensive advice. Point taken about the legality of the re-releasing idea.
The footprint tunnels could really work as there is a perimeter fence and the likelihood that the hogs use gaps which have not been repaired in recent years.
Failing that, I fully take the point that we probably need a professional ecologist to survey the area for deer and badgers as well.
Many thanks – I will update the forum when we get some news to share!