We are agreed that the referendum was advisory

No we are not. It is disputed.
It had to be challenged in court, and the appeal is yet to be heard

Keith, surely you have understood by now that the cases are nothing to do with whether the referendum was advisory and entirely to do with who is authorised to invoke Article 50: the government or Parliament?

What would it take to demonstrate this, as neither the official documents nor discussion appears to be enough. You can even read the transcript of the hearing which is perfectly clear what they were ruling on.(page 2, line 19 and following)