Author Peter Ackroyd explores Victorian London, and reveals that although the city was the thriving heart of the British Empire, it was also home to a growing underclass. He examines the story of Jack the Ripper, asking why the Whitechapel murders continue to have such a strong hold over the public's imagination, and celebrates the work of 19th-century journalist Henry Mayhew, who campaigned to give the capital's poor a voice. With Timothy West and Tom Hollander.