I ask NOT about court opinions. The UKSC doesn't publish them.
Can I get a copy of a party's 'skeleton argument' or case?
The UKSC does not publish parties' cases. [...].
Googling "Skeleton Argument of the Secretary of State" yields just 27 results, e.g.
government's skeleton argument in the Article 50 case in England and Wales, CO/1306/2016) at QBD.
Secretary of State's Open Skeleton Argument, Secretary of State's Skeleton Argument for permission renewal application, R (on the application of Campaign Against Arms Trade) v The Secretary of State for International Trade and Intervenors  EWHC 1726.