Thought it was series 3, and this is the plan for the first 5 episodes
Season 3 Episode 1
Great Yarmouth to Beccles New series. Michael Portillo learns more about the country's railways, beginning with the Great Eastern Line, which runs along the edge of England and into central London. On his travels, he discovers the grave-robbing history of Great Yarmouth and tries his hand at working a Victorian swing bridge in Reedham. He also takes to the air to reveal how a rail guidebook helped aviators during the Second World War
Season 3 Episode 2
Darsham to Felix Michael Portillo continues his journey along the Great Eastern Line, which ventures from the edge of England to the heart of London. In this leg, he examines the Victorians' fascination with Dunwich, Britain's answer to Atlantis, and discovers how Felixstowe became home to the UK's biggest container port
Season 3 Episode 3
Sudbury to Southend Michael Portillo visits the sites of Victorian freak shows, rides one of the world's first electric railways in Southend and encounters the preserved head of a medieval politician as he continues his journey along the route of the Great Eastern Line, carrying George Bradshaw's Victorian Railway Guidebook
Season 3 Episode 4
Epping to Hackney Michael Portillo travels from Epping, Essex, to Hackney, discovering why dairy herds were transported by train all over Britain, the importance of the gunpowder trade to Waltham, and details of the first murder on a train
Season 3 Episode 5
Fenchurch to Embankment Michael Portillo continues following the route of the Great Eastern Line, enjoying a ride on a miniature railway hidden beneath London. During his trip, he also rings the bells of Bow's church, and tries his hand at announcing at Fenchurch Street station