The phrase ‘muscular unionism’ is new but the concept is not.
"Muscular unionism didn’t work in Ireland in 1921 and there is no reason to expect it to work now. Ignoring the votes, and the people elected, in Scotland, Wales, and Northern Ireland, is not unionism. It’s imperialism. Dicey and other unionists were willing to countenance everything up to a Protestant paramilitary army to resist Home Rule in Ireland. And that didn’t end well either, for Britain, Northern Ireland, or indeed the Free State (now Republic) of Ireland which endured a civil war in 1922-3. Rishi Sunak would be wise to choose vanilla over muscular unionism. He should respect the entrenchment of devolution and bring section 28(8) of the Scotland Act back to life." This section states that the Westminster parliament will not normally legislate on matters devolved to Scotland.