VOCAL VIVIENNE: Madonna, whose latest single is in support of Barack Obama, isn’t the only one injecting politics in to 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, The New York Dolls and Luca Mainardi, is on sale this week in Selfridges’ in-house concept store the Wonder Room.