Referenda are binary. In/out, yes/no and it is then for the Executive to implement the results.
When we joined without a referendum in the early 70s the question was "do you think we should stay" with a Yes/No.
When the Scots, Welsh and NI had their devo vote it was a Yes/No.
With Scottish independence it was Yes/No.
It is then for the executive to deliver.
In the case of the devolved national powers and independence, those nations all have pro Independence/separatist parties.
So if the electorate do not like the settlement post referendum, they have the option to give the executive a further kick in the teeth.
It is often said that a 50% or more mandate for the SNP in an election would be sufficient to trigger and indi ref 2.
Contrast that with our membership of the EEC/EU. Any dissent to our membership could support Labour in the 80s.
But once Labour switched to a Pro EU party, even out EUing the Tories, there was no way for the electorate to express dissent, or even get a change of pace, or policy.
So we saw initially the formation of UKIP, then the referendum party formed by Goldsmith. Although UKIP was formed earlier, it only gained a foothold after Goldsmiths failed.
UKIP took votes off Labour and Tory culminating in them winning the 2014 EU election with 27%.
The public found a way to express an opinion and force the issue - it took well 10 years.
The referendum win for Leave in 2016 really was the end of UKIP.
At the 2017 GE 85% of the public voted for parties committed to a clean Brexit:
1. Leaving the single market
2. Leaving the Customs Union / committed to setting up new trade deals.
So if the established parties now stitch up an agreement to be in the SM and/or CU they will have gone back on their campaigns of only 18 months ago.
We will be back to square one in the early 90s, with a totally pro EU establishment, ignoring the direction they had been given, and no party where a vote can be cast to express one's dissatisfaction.
I sense if we had a GE and an option for "None of the Above" it would achieve a resounding victory.