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.

The original firm of Mitchell & Neilson was founded by William Neilson & James Mitchell in 1836-37 making marine and stationary engines. In 1837 the firm became known as Kerr, Mitchell & Neilson when Stewart Kerr joined the firm.

Kerr, Mitchell & Neilson was formed in 1837 when Stewart Kerr joined Mitchell & Neilson who manufactured marine and stationary engines. In 1838 Walter Montgomerie Neilson (the son of James B Neilson) joined the firm and was called on to make the business a success. By 1840 James Mitchell and William Neilson left the company, which was then effectively dissolved. James B Neilson (who had largely financed the Neilson & Mitchell venture) and Stewart Kerr formed a new company Kerr, Neilson & Co working from the Hyde Park Street works making locomotives, marine and stationary engines, but operating at a loss.

In 1840 James Mitchell left Kerr, Mitchell & Neilson and the company was renamed Kerr, Neilson & Co. Walter Neilson took the locomotive building business further, wanting to build Scottish locomotives for Scottish railway companies who until then had to go to England for their locomotives. By 1843 locomotive construction had begun. James Mitchell returned to Glasgow and ran the financial side of the business as a partner and the company became known as Neilson & Mitchell once more.

Kerr, Mitchell & Neilson became known as Neilson & Mitchell when it is believed that Stewart Kerr left the business. Marine and stationary engines continued to be made until 1855 when the company began to turn all its efforts to locomotive building. In 1855 the company became known simply as Neilson & Co.

In 1855 Neilson & Mitchell became known as Neilson & Co. Until 1858 James Reid had been the works manager at Neilson & Co. As the company turned exclusively to locomotive production, Henry Dubs who had more experience of designing & building locomotives replaced Reid. James Reid went to work for Sharp Stewart & Company in Manchester while Henry Dubs was made a partner in the Neilson & Co. business. Initially locomotive manufacturing by Neilson & Co was primarily for local Scottish railways. However, by the 1860's the company had established a large reputation in the export business, particularly in India and later in England and Europe. Later still, the company had a presence in Africa, South America and Japan. Neilson & Co also made small industrial locomotives. By 1861 the business needed to expand and so the company moved to new purpose built premises at Springburn, Glasgow named Hyde Park Works. This works eventually became the largest locomotive works in Britain. However, by this time the relationship between Walter Neilson and Henry Dubs was becoming increasingly strained. Dubs left the company in 1863 to set up his own company, Dubs & Co, taking key Neilson & Co staff with him. James Reid, who had gained a great deal of knowledge about locomotive building during his time at Sharp Stewart, returned as managing partner. By 1872 bitter resentment had come between Reid and Neilson regarding James Reid's option to buy Neilson out of the partnership. By 1876 Reid had become the sole proprietor, which continued until 1893 when James Reid's four sons became partners. Hugh Reid, the eldest son, became the senior partner on his father’s death in 1894. In 1898 the company changed its name from Neilson & Co. to Neilson, Reid & Co.

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.

Henry Dubs arrived in England from Germany in 1842 to work at the Vulcan Foundry, Warrington. He then worked for Beyer Peacock in Manchester until he was dismissed in 1857. Dubs was then appointed managing partner at Neilson & Co in 1858, replacing James Reid (later of Neilson, Reid & Co). By 1863 the relationship between Dubs and Walter Neilson had effectively broken down and Dubs established his own company, Dubs & Co. By 1864 the company had established the Glasgow Locomotive Works at Queen's Park, Polmadie, Glasgow. Dubs took with him from Neilson & Co key staff, including chief draughtsman Sampson George Goodall-Copestake. The new company effectively competed with Neilson & Co for customers and very quickly established a thriving business. In 1867 Dubs & Co began building locomotives for export. Initially orders were received from India, Europe, Russia and later New Zealand and China, while still building a significant reputation in the domestic market. In 1866, Dubs & Co became one of the first companies to employ women as tracers in their drawing offices. Henry Dubs died in 1876 and was succeeded by William Lorimer. When the company became part of the North British Locomotive Company in 1903, Dubs & Co employed 2000 people and was producing on average 160 locomotives a year. The works became known as the Queens Park Works at amalgamation.

Sharp, Roberts & Company was an engineering, machine and locomotive manufacturing firm formed by Thomas Sharp and Richard Roberts. The original company, Sharp Roberts, was founded in 1822. The company intially had its premises at Globe Works, Faulkner Street, Manchester before moving to Atlas Works in Great Bridgewater Street, Manchester. In spite of the products from the firm being known as "Sharps" or Sharpies it is Roberts who provided the dominant engineering skills. The first locomotive was constructed for the Liverpool & Manchester Railway, a 2-2-0: No. 32 Experiment. Three similar locomotives were constructed for the Dublin & Kingstown Railway. These early products suffered from steam leakage from the vertical cylinders and these were subsequently abandoned. In the new design the cylinders were placed under the smokebox and the 2-2-2 type was adopted with outside frames with additional inside bearings for the driving axle, and a combined dome and safety valve fitted near the chimney. Ten of this type were supplied to the Grand Junction Railway in 1837. 600 of this type were made between 1837 and 1857 and were supplied to France, Italy, Germany, Belgium, Holland, Russia and Spain. In 1843 Roberts left the firm and it became Sharp Bros.

In 1843 Richard Roberts left Sharp, Roberts & Company, and the company became known as Sharp Bros. In 1852 John Sharp who was the senior partner retired & Charles Patrick Stewart took over. The name of the company was consequently changed to Sharp Stewart & Company.

In 1811 the firm Sharp, Greenleaves & Co had premises in New York Street with a Warehouse at Oxford Street Wharf in Manchester. c.1822 the Sharp offered Richard Roberts a partnership and the firm became Sharp, Roberts & Company, Engineers, Globe Works, Faulkner Street. In 1825 Roberts invented the self-acting spinning mule, and by 1833 the company's first locomotive was built for the Liverpool and Manchester Railway. In 1843 Richard Roberts left and the firm became Sharp Bros. In 1852 John Sharp who was the senior partner of Sharp Bros. retired and Charles Patrick Stewart took over. The name of the company was consequently changed to Sharp, Stewart & Company, becoming a limited company in 1864. Throughout the 1850’s – 1880’s, Sharp Stewart made locomotives, but also continued to make machines, tools and carry out foundry work. The company soon needed bigger premises as orders for locomotives increased significantly and the lease on their Atlas works site in Manchester was due to expire. By 1887 the Clyde Locomotive Company was for sale and Sharp Stewart decided to move its business to Glasgow where wages and rates were lower than in Manchester and where they would also have access to sidings and docks at the site of the Clyde Locomotive Works. Walter Neilson sold the Clyde Locomotive Company to Sharp Stewart who renamed the works the Atlas Works after their old premises in Manchester. The move to Glasgow was completed by 1888 and within a short period of time, work in Glasgow began to exceed production levels Sharp Stewart had been achieving in Manchester. Orders for locomotives came in from all over the world, predominately from Asia, South Africa & South America, as well as the domestic market and industry. When the company became part of the North British Locomotive Company in 1903, Sharp Stewart & Co Ltd employed 2000 people and was producing on average 150 locomotives per year. By this time Sharp, Stewart had produced over 5000 locomotives. The works retained the name Atlas Works at amalgamation.

The company was founded by Walter Neilson in 1884 after leaving Neilson & Co. The Clyde Locomotive Works was established at Springburn, Glasgow, across the railway line from Neilson & Co’s Hyde Park Works. The company was not a success (completing only 23 locomotives) and was taken over by Sharp Stewart & Company in 1887.