Cameron's policy of offering a referendum in 2015 as an electoral tactic was a stupid political move in my opinion, he learned the wrong lesson from the Scottish independence referendum in 2014 and gambled the future of the country not out of any democratic principle, but for short-term domestic expediency. The referendum was a fundamentally ill-conceived thing, it was a knee-jerk reaction on the part of the Conservative Party who feared a) that Cameron could not maintain discipline over the right of the party and b) that the Conservatives would bleed voters to Nigel Farage's then-party UKIP to the right.

I'm not opposed to voting on EU membership in general, but the way the actual referendum was conducted was poor and it's increasingly clear that Russia attempted to interfere with it as well. Compare it to the Scottish referendum which was pretty well-conceived, the Brexit referendum looks amateurish in comparison. The reason is because it had very little to do with the government suddenly sprouting a love of participatory democracy, and everything to do with Cameron thinking that because he had won one referendum and ostensibly stopped the Scottish nationalists for a generation he could do the same to UKIP and the right of his own party.

In my view the vote should have been held, a democracy is only a democracy if it's allowed to make potentially harmful decisions for itself. However it should not have been rushed into being with zero regard for how it might test the constitution or what a leave vote actually meant, in my view the consequences of a leave vote should have been characterised and defined well in advance; all the debate between 'hard Brexit' or 'soft Brexit' should have happened before the date of the vote was set. It also should have been more credibly secured against Russian influence in light of the threats to democratic integrity that were new at the time, the government appears to have been genuinely lax on this front. They couldn't have carried it out in a more division-generating way if they'd been trying in my opinion, and it's because they rushed it for risky party-political reasons.

That's kind of my point. Constitutionally speaking, the Brexit referendum was advisory and could have been ignored. That would have been completely unconscionable from a legitimacy point of view though, so whatever the constitution has to say on the subject on paper an iron-clad democratic mandate to carry out Brexit was forced to coexist with Parliament's iron-clad supremacy.

This is why I think it was constitution-breaking, the constitution simply isn't set up to gracefully deal with a conflict between 'Brexit must happen' and 'Parliament cannot agree on how to carry out Brexit'. All of this against the ticking clock of Article 50 as well. Instead Boris Johnson ended up brute-forcing his way through the issue with the 2019 election and the purge of his non-Brexiteer MPs. The system did ultimately hold up (even in the face of Johnson's prorogation crisis), but I think Cameron was very irresponsible. Not for holding the referendum, but for not figuring out all the potential complexities of a leave vote before calling the referendum. The constitution got an uncontrolled stress test that didn't need to happen the way it did.

Also to add to that, the limits of Parliamentary sovereignty really were tested with respect to things like the Northern Ireland peace agreement during the Brexit negotiations.