Flying Scotsman was built in Doncaster, the first locomotive of the newly formed London and North Eastern Railway (LNER). It left the works on 24 February 1923 with number 1472. It was designed by Sir Nigel Gresley as part of the A1 class—the most powerful locomotives used by the LNER at that time.

By 1924, when it was selected to appear at the British Empire Exhibition in London, the loco had been renumbered 4472—and given the name 'Flying Scotsman' after the daily 10.00 London to Edinburgh rail service which started in 1862.

The British Empire Exhibition made Flying Scotsman famous, and it went on to feature in many more publicity events for the LNER. In 1928, it was given a new type of tender with a corridor, which meant that a new crew could take over without stopping the train. This allowed it to haul the first ever non-stop London to Edinburgh service on 1 May that year, reducing the journey time to eight hours.

In 1934, Scotsman was clocked at 100mph on a special test run—officially the first locomotive in the UK to reach that speed. The test run proved to the LNER's directors that steam power could provide high speeds, negating a plan for the company to use diesel power on its high-speed services.

LNER passenger locomotives had always been painted Apple Green. But during the Second World War, Flying Scotsman was repainted in wartime black, in common with all railway stock. After the war, it became green again and was rebuilt as an A3 Pacific.

In 1948, British Railways was formed and rail travel in Britain was nationalised. Scotsman, now numbered 60103, was painted blue for a time, then BR Green.

It remained this colour until 1963, when it was retired by British Rail. By this time, it had undergone several alterations to improve its performance—but it had been pulling trains for 40 years, and steam engines were becoming old-fashioned.