VOCAL VIVIENNE: Madonna, whose latest single is in support of Barack Obama, isn’t the only one injecting politics into pop music. Vivienne Westwood is tossing her hat into the ring, too: “I’ve written a political song about the legalized, 42-day detention of suspected terrorists,” said the designer at the London launch of her compilation CD at Selfridges on Monday. “I never listen to the radio, but I had to recently to see who’s out there to sing it. I didn’t like any of them! So it looks like I’ll have to. I’m not a singer, really, but I’ll do something.” Westwood’s CD, “Catwalk Breakdown,” a selection of favorite tracks by everyone from Tchaikovsky to The New York Dolls and Luca Mainardi, is on sale this week in Selfridges’ in-house concept store, the Wonder Room.