They came in their thousands to venerate the true Queen of Scotland. While Brenda was kicking off her ceremonial pumps, Shirley Manson was holding court in Edinburgh's Princess Street Gardens. "Well, who'd ah thunk it?" said the girl in the orange puff-ball jacket. "I never thought I'd see the day. A parliament after 300 years. You should be proud of yourselves."

They were, in a weary way. This was a space filled with the finest of Edinburgh's middle youth, who'd clearly had quite enough, thank you, of over-orchestrated pomp: if the Scottish parliament rocks, went the murmur, let it start rocking here. And, to general surprise, Shirley Manson and Garbage totally realised the moment.

"This is my city," said Shirley. And this is why her performance was so appropriate: despite her tenure at the Advanced Institute of American Neo-Punk that is Garbage, Shirley let her Scottishness rip. "I never get to do this," she giggled, as she launched into another lengthy Caledonianising of Garbage songs that you thought were, well, just Garbage songs.

I'm Only Happy When It Rains was prefaced as "a comment on the Scottish national psyche". A raggedy performance of Lennon's Don't Let Me Down was dedicated to "all those SMPs who put their bums on parliamentary seats tomorrow morning". And quite the most spine-tingling moment was when she sang a version of Robert Burns's John Anderson, My Jo, wrapped in a saltire chucked from the crowd, accompanied on guitar by Duke Erikson. "My mum sang this to me when I was three it's when I first learned to love melancholy songs."

And she sang it well - but with some weird electronic harmoniser on her voice, folk meeting techno. And if Garbage could be read as any kind of metaphor for the Scottish parliament, it was in this moment. Totally herself (Edinburgh wide-girl made good), in a totally global context (surrounded by American musos-in-overalls, playing with laser precision). Wouldn't most of the politicos love to display this level of competence with flair?

Although when the lads at the front started shouting "Shirley, Shirley", she nearly donned the tartan bonnet. "Don't be nice to us, you'll totally dismantle us hey, is that ma old boyfriend there in the front row?" Shirley, Queen of Scots: an automatic coronation.