In Federalist 69, Alexander Hamilton makes much of the "absolute negative" that George III had over parliamentary legislation. I've often described this argument as a bit of a strawman, since by 1788 it had been 80 years since the crown refused to grant royal assent. I wonder, however, if I'm giving too much evidence to hindsight.
Did Englishmen of Hamilton's day have any reason to see withholding royal assent as an active power that the king might plausibly exercise? Were there any close calls? Did the 18th century kings use the threat of withholding assent to influence Parliament?
The king of Great Britain, on his part, has an absolute negative upon the acts of the two houses of Parliament. The disuse of that power for a considerable time past does not affect the reality of its existence; and is to be ascribed wholly to the crown's having found the means of substituting influence to authority, or the art of gaining a majority in one or the other of the two houses, to the necessity of exerting a prerogative which could seldom be exerted without hazarding some degree of national agitation.
Hamilton is saying essentially
As for the "plausibility" of using it, the possibility of it being used was plausible in 1788, and still is today. In the era Hamilton wrote, George III opposed Catholic Emancipation on the grounds of it violating his coronation oath, this delayed its passage even after the Union with Ireland in 1800, his son and successor George IV only very reluctantly agreed to give assent, in 1829. 85 years later, George V seriously considered using it for an Irish home rule bill, he decided not to unless he had "convincing evidence that it would avert a national disaster, or at least have a tranquillising effect on the distracting conditions of the time". A century later during the debacle that was Brexit, when Parliament and the executive fought openly over control of Brexit, which culminated in the dispute over the European Union Withdrawl (no 2) Bill, the so-called "no-deal Brexit bill", there was serious talk about the Government advising the Queen no to grant Assent, I realize this last part violates 20-year rule, but its done to illustrate that the power still exists and has been considered for use even recently.
References
*Bradley, A. W. & Ewing, K. D. (2003). Constitutional and Administrative Law (13th ed.)
*Gay, Oonagh; Maer, Lucinda ( "The Royal Prerogative" ). House of Commons Library.