My client rented a room in his Aunt's house for £200 /month. It was fairly informal - Aunt had never let property before. At the time of the HB claim they had a rent book but no tenancy agreement; there are no arrears as client can (just) afford rent out of his benefits (IS & DLA). The LA called them in for interview at which they realised that a tenancy agreement was a good idea so they subsequently obtained one.

We lost the tribunal. The judge decreed that the initial arrangement was not commercial. Is this an error of law? If so we would have a better chance of success at a new tribunal if the final arrangement is looked at.

Any thoughts greatly appreciated.

The finding of itself is not an error of law. You need to look at why and how the finding was reached. What, for example, was the evidence used to support such a finding? Where any irrelevant considerations taken into account which materially affected the decision? Where any relevant considerations omitted. Where there sufficient findings of fact? Was the legislation propery applied? These are just examples. Have you the statement of reasons yet? That is the starting point.