>[The PM] does not have any of the powers required to prepare that notice so it is legally binding.
Is that relevant?
The question is whether the rest of the EU decides article 50 has been invoked and from their point of view, a simple statement is sufficient. Assuming they think its been done, it happens automatically. I don't see how what the UK courts think is relevant or what they could do - impose their will on the French and the Germans? What would they do? Interfere with internal UK affairs? I think we just had a referendum about that.