Based on the K class for mixed traffic, Reid commissioned the J class for express service. Like the first series of the K class, the J had a wheel diameter of six feet six inches. The dimensions of the cylinders were also the same. In order to be able to run the line from Edinburgh to Carlisle non-stop, they received a larger tender and a smaller boiler. From the original design, which was designated as D29 by the LNER from 1923, six were made in 1909 and another ten in 1911. They were named after characters from Sir Walter Scott's stories, which is why they were also known as the “Scott Class”.

Also in 1911, two more machines were built with a superheater of the Schmidt type, which were later designated as the D30/1. For operation with superheated steam, adjustments were made to the arrangement of the piston valves, which led to a higher position of the boiler. Between 1914 and 1920, further 25 production machines were built, this time with superheaters of the Robinson type. These became the D30/2 at the LNER.

No. 896 “Dandie Dinmont”

Locomotive Magazine, September 1909

As early as the 1920s, the D29s were increasingly being used for stopping services, fish trains and as pilots, while the D30s continued to be used for express trains. Nothing changed when most D29s got superheaters between 1925 and 1936. After that, the rebuilt ones were called D29/2 and the non-rebuilt ones D29/1. In the 1930s they were increasingly relocated to more rural regions. When British Railways was founded in 1948, a total of 35 class J locomotives were taken over. The last D29s were retired as early as 1952 and the D30 only between 1957 and 1960.