Chris

I don't think they can, not now the question is open. A court ruling limiting the Royal Prerogative isn't something the government can just leave halfway up the court system. The prerogative is, essentially, the means by which the British government gets away with doing anything that hasn't been explicitly authorised by Parliament. If it's a critical constitutional issue - and it is - then it has to be pursued to the end. The outcome is likely to be cited in any and every future challenge to the boundary between the powers of Crown and Parliament so it has to be settled decisively now.