I have a case coming up at the Commisioners where this is an issue. Amongst the papers is Capello v. Secretayr of State for Work and Pansions in the Court of Session which was a judicial review of refusal of leave to appeal. Am I right in thinking this is not binding on the Commissioner?

Yes it's not binding because it appears to be a Scottish case. Although it can be used as a pursuasive argument.

It is a bit stronger than that. For reasons of "comity and practicality"
Commissioners in Scotland will follow the Court of Appeal and Commissioners in England will follow the Court of Session unless the
Courts at that level are in conflict in which case they would follow their local superior court (page 237 vol 3 social security legislation 2004).

From memory the Court of Session was not invited to consider whether or not the amendments were ultra vires so the view they express on
what the regulation means may be distinquished for that reason.