I don’t think that it’s a question of the “left” having forgotten basic principles. But there is an important point buried in @giles_fraser’s piece about the way in which those who support constitutional checks on executive power/human rights protection frame their discourse. https://twitter.com/giles_fraser/status/1380036432908189697

At a technical level, Magna Carta is mostly no longer law (though the bit Giles quoted still is) and even those bits of it that are law have uncertain legal effect.

It is also far from what anyone would now regard as an adequate statement of limits on executive power: nothing on speech, family life, assembly, freedom of religion (protecting the rights of the C of E excepted)... But lots on arcane property rights (fish weirs...)

But it does contain statements of principle that are radical in implication. The right to due process before being imprisoned or stripped of rights: try applying that to (eg) those stripped of citizenship by a minister’s order.

Moreover, Magna Carta’s place in England’s historical imagination is huge. It served - from Kett’s Rebellion, through the English Revolution and on, as a model of how subjects could force the Crown to accept binding limits on its power. The myth is, in many ways, what matters.

Though a charter for nobles, it helped create the story of the “free born Englishman”: a man (well, of course, at that time) who had status and rights by virtue of citizenship that no King or powerful noble could remove: rights that he could go to law to protect.

There is a tendency among the liberal left to assume that human rights charters, and ideals of the executive as being subject to law and vulnerable to legal challenge, are products of the Enlightenment: things that we can deduce from philosophical reasoning.

One can debate the history of ideas and the political philosophy: but (in England) it is also worth thinking about how you can frame human rights principles and limiting the powers of the state as things that are deeply rooted in English culture, history and religious traditions.

After all, in England, successful movements for political and constitutional reform (as well as heroic failures) have typically used language taken from English history to frame radical principles.

Strong statements of rights against the executive and demands for executive accountability are put forward as a restoration of former liberty against recent usurpation and abuse.

None of that is to say that those who delude themselves and others by claiming that Magna Carta is law and protects their “rights” when it isn’t and doesn’t shouldn’t be corrected (and pointed in the direction of the Human Rights Act, particularly when they are HRA-sceptics).

But there is also nothing wrong in looking outside the HRA, and to English history and the common law, to frame arguments about rights and checks in executive power.

(Indeed, there are many recent cases where our courts have done precisely that, finding constraints on executive power in common law principles rather than in the HRA.)

And there is no reason why Magna Carta - and the movements inspired such as the Levellers and Chartists - can’t inform the language of a campaign for checks on executive power and for real democratic change in the way in which we are governed.

After all, the brilliant part of the Brexit slogan - the most successful campaign for fundamental constitutional change in our recent history - wasn’t “take control”: it was “take *back* control”.