Unfortunately I have not had the chance to read through the entire volume of The Invention of Scotland. Nonetheless from what I could gather in his earlier essay The Highland Tradition of Scotland, his arguments were that much of highlander tradition were manufactured following the union with England to foster national unity and separate their culture identity from that of Ireland.
Knowing the amount of controversy surrounding a number of books by Trevor-Roper, how do historians view his stance on Scotland? Are there any good counter-arguments to read?
The most important thing to keep in mind when reading Lord Dacre (as he is now known) is that he was a fervent anti-devolution supporter and his politics influenced the way he even approached the topic of Scottish History. It's telling to note that with the emergence of some really good scholarship from the Universities of Edinburgh and Glasgow (think scholars like Professor Wilson MacLeod and Professor Dauvit Broun), Trevor-Roper stopped publishing new material along the lines of his old arguments.
For the most part, historians of Scotland tend to treat these essays and the collection/edition of them into The Highland Tradition of Scotland with resignation laced with contempt. Although Lord Dacre is an engaging and witty writer, his argumentation is overly simplistic and incredibly biased.
For more reputable work on Scottish culture and history, you really want to pick up books or articles by any of the following scholars: Dauvit Broun, Martin MacGregor, Steve Boardman, Julian Goodare, Michael Brown, Michael Lynch, Alison Cathcart, Katie Stevenson, G.W.S. Barrow, John Bannerman, Jenny Wormald, Sir Tom Devine, and Ewen Cameron. (There are more but I think that's a sufficient list to get you started) :)