Plot: Lauren Laverne meets fashion designer Matthew Williamson ahead of his upcoming exhibition at the Design Museum, and Andrew Graham-Dixon visits the Tuscan city of Siena to assess its role in the Renaissance. In Reykjavik, Verity Sharp talks to Icelandic band Sigur Ros about their film Heima, which focuses on the group's series of unannounced gigs performed across their home country in 2006