I doubt if the invention of the Whig version of history was entirely the work of Buchanan and other Scots historians. In short, this is an enlightening and entertaining work, but one misses its companion piece: The Invention of England.
One may question Trevor-Roper on particular details, but two general points should be made. First, he writes of the Scots as Celtic and the English as Anglo-Saxon, which is no longer a tenable opinion; both are mongrel peoples. Second, he denies to the Anglo-Saxons (that is, the English) the mythopoeic faculty. “All the myths of England come not from the Anglo-Saxons, but from the Celts,” he writes. Perhaps so, but the English adopted Brutus and his descendant Arthur and made these myths their own. They may also have imbibed the myth of Merrie England from Scott’s Ivanhoe. Moreover, in the 16th and early 17th centuries, they devised their own myths: of the fiercely Protestant sea dogs who destroyed imperial Spain (the credit for doing that should really go to the Dutch and the French); and the myth of the ancient (Saxon) constitution, later subjected to “the Norman yoke”, which English judges elaborated to justify opposition to Stuart “despotism”.