HMRC need to sit it out...
If HMRC joined in as a plaintiff, and the case is lost, then they are on the hook for a share of the winers costs. Why would they want to expose themselves to that, if they thought the plaintiff was doing a reasonable job, (or though that the case was a lost cause, so don't care if the precedent goes against collecting the tax that they don't consider due)
Biting the hand that feeds IT
