Sadly the improvement was temporary. This morning he was extremely poorly and a visit to the vet confirmed a sizeable abdominal tumor and secondary pneumonia. The antibiotics helped him rally from the pneumonia, but the end was inevitable. Poor lad has been euthanised.
Still, the time he spent has made us think about building a proper enclosure and buying a breeding pair at some stage in the future, with plans to free range them once they settle in.
A huge thank you again to all for your help