In Great Britain, the Victorians built the vast bulk of the country’s railway system and   constructed steam locomotives to work them - many different designs were created, with many different results. The final form of the steam locomotive was seen in the designs introduced in the early years of the 20th century, from there on development was in detail and power.

Using footage from the last quarter of a century, this programme looks at the way this final form was refined by some of the most famous engineers of their time, right up to the last steam locomotives built for main line service in the country.

This is The Jazz Age, examining the locomotives of the 1920s.

Following the Great War, the railways of Great Britain firstly had to renew war damage and then had to re-group, forming four large companies from 1923, known as the "Big 4".

We follow the progress of locomotive design as each of the "Big 4" developed its own style - although no-one would notice any change on the Great Western! The Southern Railway’s management was intent on electrification so most of its new locomotives were just developments of its constituents’ designs, whilst on the LMS pre-grouping rivalry simply continued as did the pre-grouping designs - with one or two notable exceptions.

Only on the cash-strapped LNER was there any real development - it was fortunate to have acquired the great Nigel Gresley to create a modern steam fleet.