Michael Portillo continues his journey from Southampton to Wolverhampton beginning today in Chippenham, where at Lacock Abbey he discovers how the world's first photographic negative was made and learns how to make a print. He travels on to Bristol to visit the Victorian Clifton Zoo, where he finds tigers and polar bears before him also arrived by train. Next stop is Severn Tunnel Junction in Wales, where he explores an extraordinary piece of Victorian engineering with its own pump house pumpin...