and on the other a BBC report of what the government legal advisor said during an interview, I am more inclined to regard the former as more reliable.

Read it again. It is not from an interview it is the government's case as put to the High Court.

Yes, I made a mistake. I misread it as the BBC interviewing the government lawyer and him explaining his case, rather than a BBC report of what was said in court. My error, fully admitted.

Which does not change one iota that the argument was about who had the right to invoke Article 50, and not a claim the referendum is binding.

We could go further: exactly the same issue would arise even if there had not been any thought of a referendum. It would still be necessary to clarify who invokes Article 50.