The last bill that was refused assent by the sovereign (on the advice of ministers) was the Scottish Militia Bill during Queen Anne's reign in 1708.

https://en.wikipedia.org/wiki/Royal_assent

This leaves us with a clash between two important and well-established rules, which normally pull in the same direction (I’m being charitable to Ekins and Laws, as the better view is probably that the first of these rules does not apply to the legislative context): 1. the monarch ought to act on ministerial advice; 2. the monarch ought not to withhold assent to legislation.
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When we talk about supremacy we mean who has the authority to legislate: not who gets to draft the laws, but who gets to decide what counts as law. The situation that Ekins and Laws imagine is one marked not by failure or stasis – in which, for instance, no parliamentary agreement can be found (the situation we are still in fact in). In their scenario, legislation has been passed by Parliament, if in a politically – but not legally – unconventional way. What is said to justify overriding fundamental constitutional principle is the attempt by the Commons to seize power from the government. Constitutionally, there is no injury here to redress, for the simple reason that the relevant power – the constitutional authority to pass laws – was never the government’s to lose.

What Ekins and Laws suggest, in effect, is getting the monarch to thwart Parliament in the interests of the executive. At the level of principle, this is little short of monstrous. It invents for the 21st-century executive, out of the archaic form of the monarch’s ‘negative voice’, a power to veto legislation. They invoke a principle that the law should not be changed until both the government and Parliament have agreed that it should be. There is no such principle. The claim confuses the normal with the norm, how legislation is typically passed with the rules that govern the process: whether or not a statute is proposed by government is immaterial. It also assumes that the UK executive has a separate source of democratic legitimacy, like the elected (and veto-wielding) US president. But in the Westminster system, democratic authority is channelled through Parliament. Constitutionally speaking, we vote for MPs and a government is formed from among their number.

The proposal, flimsy and fanciful, may be risible as a constitutional proposition. But it is no joke. There is a serious undercurrent to all this. What animates the Judicial Power Project, with which Ekins is intimately associated, remains unclear. But it is not only the rise, as they see it, of judicial power. As Ekins’s writings on Brexit display, its targets seemingly include any institutional check on executive power, political as much as legal. This is not, to my mind, a programme of constitutional conservatism in the spirit of Blackstone or Burke. It is an anarcho-conservatism more familiar from the work of counter-revolutionaries such as Carl Schmitt. Authoritarian rather than conservative in disposition, it treats established constitutional forms and norms as fungible, even disposable, and presses exceptional moments in the direction of a central authority delivering the ‘will of the people’. For all the constitutional posturing, the object of the power so directed is to make it easier to realise a purified version of an imagined past.

https://www.lrb.co.uk/blog/2019/april/the-executive-power-project