In 1898 the company changed its name from Neilson & Co to Neilson, Reid & Co. When the company became part of the North British Locomotive Company in 1903, Neilson, Reid & Co employed 3500 people and was producing around 200 locomotives a year. The works retained the name Hyde Park Works at amalgamation.

The North British Locomotive Co Ltd was formed by the merger the 'big three' Glasgow locomotive builders (Sharp Stewart & Co, Neilson, Reid & Co and Dubs & Co) in 1903 as a result of increased competition both at home and from abroad. The new company claimed to be the largest manufacturers of locomotives anywhere outside America and was prompted by the ever increasing annual production by the Baldwin Locomotive Company in Philadelphia, USA, which had recently made incursions into the domestic UK market and in India, which the British locomotive industry had considered to be its own special preserve. It was believed that the rivalries and competition between the three companies operating individually within Glasgow had already produced significant technological advances which, in the new North British Locomotive Company would combine to make a single powerful and well equipped company, ready to dominate the market and take on competition, particularly from America. The new company never managed to operate at its capacity of 700 locomotives per year, producing a maximum of 573 in 1905. These numbers were maintained through to 1909 when production numbers began to fall rapidly. During the First World War North British Locomotive Company made locomotives for the War Department, as well as munitions and other military equipment, which were produced in vast quantities to meet the high demand. However, between the two World Wars, while orders were still being received, particularly from domestic railway companies, the fluctuation of demand meant that the company ran into some difficulty. As a result, employee numbers were significantly reduced, and manufacturing was concentrated at Queens Park and Hyde Park works. The last locomotive orders were completed at the Atlas Works in 1923. The Great Depression from 1929 saw the decline in demand for locomotives worldwide, with none built at all in 1932, and by the end of the 1930s, locomotive production at the North British Locomotive Company was operating at a loss. At the outbreak of the Second World War the company concentrated once more on war work, supplying both locomotives for the Ministry of Supply and munitions for the war effort. After World War II there was something of a revival in locomotive manufacturing, with orders being received and agreements being reached to build diesel & electric locomotives with the General Electric Company. This upturn in fortune was not to last however, as the North British Locomotive Company failed to make the successful transition from steam to diesel locomotive production. In 1957, the last order for steam locomotives was placed with the company and the last steam locomotive was completed in 1958. Although the company were making small industrial diesel locomotives, and received some early main line diesel orders from British Railways, the orders were never big enough to maintain the company. Other locomotive manufacturers, who had acted swiftly in transferring from steam to diesel and electric production, were becoming more successful. The company went into liquidation on 19 April 1962 with Messers Andrew Barclay Sons & Co (Kilmarnock, Ayrshire, Scotland) acquiring the North British Locomotive Company's goodwill.