> constitution-breaking and divisive referendum

What part of the constitution does a referrendum break? One of the main principles of British constitutional law is that Parliament is supreme.

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.