While I do agree that there was the Mixed Government issues, long established in Britian, that underlaid the evolutionary (as opposed to metaphysical) view of government and politics, I do think that at the end of the 18th century they were about to be swept up by the enlightenment metaphysics. Hence the break of the New Whigs from Burke's self styled Old Whigs.
I guess my point might still stand if it is judged that the anchoring influence of those three large minds and their adherents and lesser allies were the "if-but-for" influence that kept Fox and the others enamoured with metaphysical constructs of government at bay.
The unwritten constitution may have been abandoned at that point, if-but-for the strong buttressing that was done in the face of the Enlightenment....will you buy that much?
I still return to my reading last year of chapter four in Hayek's Constitution of Liberty and his differentiations between the Evolutionary Constitutional Democracies (Rule of Law) and the Totalitarian Rationalistic Democracies. Here was the point in time when that was averted in our heritage, although, we have continued to fight it off every year since.
The Germans did not have that heritage, or those anchors and started down the path to excess despite the example of the French--hence the article.