"There are no provisions in the EU Referendum act to formally set out what would happen in the event of a vote to Leave the EU. "
Because that wasnt neccesary. Those terms have already been agreed by the Lisbon Treaty.
Comparison to the AV referendum is a moot point, as membership to the EU has clearly been defined in the previous treaties ratified. Exiting those treaties are subject to the agreement we gave to the EU when entering.
To argue the terms of exit, on a previously ratified treaty ( .....is indeed, gate, horses, bolt) but would indeed have required an act of parliament on referenda, to ask to change terms of a previously ratified treaty. That would be impossible to do, as our contract is with the EU. A member state, cant just, after the event, decide they dont like the terms, hold a referendum, have a vote, then dictate to the other party (the EU) that they (the EU) must bow to the now 'law' of that member state, and vary the terms of the original treaty. The only way to vary the terms, is to get full agreement from all member states. This is why, Labours manifesto promise on a referendum BEFORE we signed Lisbon was so important. They were elected, based on that promise. A representative parliament must be exactly that, representative. However, the subsequent legal challenge to Labours U-turn failed as the court judged a manifesto promise is not legally binding.
When people talk about a constitutional crisis. This is the mess we are in. A manifesto is not enforceable as the basis of what you are 'representing'. (We digress)
The AV referendum indeed needed to clarify the position on 'decision' as that very position was being upheld by the decision it was being asked to make. A constitutional change would have had to be made if the AV vote had succeeded.
There was no requirement to change our constitution by deciding if we wanted to continue with our contract with the EU or not. HOWEVER, due to those very 2 important legal challenges, a/ on manifesto (no party was going to xhallenge this further as who on earth wishes to keep to manifesto promises?) and b/ on Miller, it is absolutely right that TM now gets the highest direction from the Supreme court to clarify. Whilst the initial act wouldnt change constitutional law, the judgments subsequently do.
The Miller case was simply to ask to clarify the PMs right to use Royal prerogative. Now that is a whole different debate, but yes, as it now stands, our judiciary are in place by the very prerogative the miller case has over ruled.
To say, the 2015 EU Referendum Act stated it was "only advisory", is wholly incorrect.