Trains

When he was a child, Gregg loved playing with toy trainsets. Now he's got special access to learn how the ultimate model is made: a huge 187 tonne, five carriage electric train. At the 84-acre Alstom factory site in Derby, each one takes up to one thousand hours to complete.

Gregg follows every step of the process, from the delivery of vast lengths of aluminium and a 15,000 degree welding operation to the carriages' assembly with a set of enormous cranes. He learns about such parts of the train's design as the dead man's pedal and the importance of electrification - all before getting to drive the newly finished train himself.

Meanwhile, Cherry Healey travels to Scotland to visit the UK's last remaining factory that produces aluminium via smelting. She also visits an HS2 construction site to learn how two huge tunnel boring machines are digging ten miles through the hills.

Historian Ruth Goodman is energised by the history of electric trains as she learns that the UK's first was a tourist train that is still in use along the Brighton seafront. The technology pioneered in the seaside town went on to be used in underground transportation all over the world.