In March 1936 Britain sold Mesopotamian Railways to Iraq, which renamed the company Iraqi State Railways (ISR). In 1958 ISR was renamed Iraqi Republic Railways.

In 1937 Robert Stephenson & Co. Ltd purchased the locomotive department of R & W Hawthorn Leslie & Co. Ltd. They became Robert Stephenson and Hawthorns Ltd. The policy was to concentrate the building of main line locomotives at Robert Stephenson’s Darlington works and industrial locomotives at Forth Banks. In 1944 Vulcan Foundry acquired Robert Stephenson and Hawthorns Ltd, ending Hawthorns' 137 year connection with Forth Banks. In 1955 Vulcan Foundry became full members of the English Electric group of companies, which became part of the GEC group of companies in 1968.

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.

In 1854, Charles Frederick Beyer and Richard Peacock founded Beyer, Peacock & Co, a mechanical engineering company. Their works were at Gorton, east of Manchester. A legal partnership was formed between Charles Frederick Beyer, Richard Peacock, and Henry Robertson, a sleeping partner which took effect from 1 January 1855. In the early days of the company it was the partners who managed the affairs of the company. Beyer acted as Chief Engineer with control over the Drawing Office and Works, Peacock as Commercial Manager handled the commercial side of the business, and Robertson acted as Financial Advisor. Under the Chief Engineer were the Chief Draughtsman and the Works Manager. An accountant was also employed. In July 1855 the first locomotive engine left Gorton. It was made for the Great Western Railway Company and was used on the Paddington to Oxford route. Between 1854 and 1868 Beyer, Peacock built 844 locomotives, of which 476 were exported. The company sold mainly to the colonies, South Africa and South America, but never broke into the North American market. In 1883 the company was incorporated as a private limited company and renamed Beyer, Peacock & Co Ltd, with registered offices at 34 Victoria Street, Westminster. In 1902 the company became a public limited company, Beyer, Peacock & Co (1902) Ltd. (The (1902) was dropped the following year). In 1908 the registered offices were moved to Gorton and the new London office was at 14 Victoria Street, Westminster. In 1919 the London offices were given up and then in 1923 new premises were acquired at Abbey House, London. During WWII the registed offices were moved to Flore Manor in Northamptonshire. In 1956 the London offices of the company were moved from Abbey House to Locomotive House, Buckingham Gate. One of Beyer, Peacock's most successful locomotives was an articulated locomotive called the Garratt. Its designer, H. W. Garratt, had a wide knowledge of locomotive design and construction from his work in various countries including Argentina and Cuba. In 1908 Garratt was granted a patent. Beyer, Peacock had sole rights of manufacture in Britain. In 1928 the patents ran out and the company began to use the name Beyer-Garratt to distinguish their locomotives. During WWI Beyer, Peacock began to manufactire artilliery and in August 1915 Gorton Works was put under Government control with production switching almost entirely to the war effort, especially heavy field artilliery. During WWII the company was again brought under government control but continued to build locomotives throughout the war. Beyer, Peacock was faced with competition from tramways and electric railways. They began to look for alternatives so that they were not dependent on one product. In 1932 they acquired Richard Garratt Engineering Works Ltd who made steam traction engines, steam road lorries, and agricultural equipment. In 1949 Metropolitan-Vickers, Beyer, Peacock Ltd was formed which was jointly owned by Metropolitan Vickers and Beyer, Peacock. The company was created to build locomotives other than steam. By 1953 Beyer, Peacock had acquired the following subsidiary companies: Denings of Chard, makers of agricultural machinery; Theramic Ltd, makers of theramic siphons for locomotives; Maiuri Refrigeration Patents, Low Temperature Developments Ltd, and some other companies concerned with sales, such as Rail Traction Supplied Ltd. In 1957 Beyer, Peacock acquired Anti-attrition Metal Co and in 1958 Air Control Installations Ltd. In this year Beyer, Peacock (Hymek) Ltd was formed. The late 1950s saw a rapid transformation in locomotive manufacture. In 1955 British Rail decided to switch from steam to diesel and overseas users followed suit. Beyer, Peacock all but closed down the Gorton plant at the end of 1958. They had chosen to make diesel-hydraulics but British Rail opted to use diesel-electrics. In 1960 Beyer, Peacock’s subsidiary companies became members of the Beyer, Peacock Group and Beyer, Peacock Co. Ltd became the holding company. In 1966 all production ceased at the Gorton foundry. Shares in Beyer, Peacock were eventually bought by National Chemical Industries Ltd and in 1980 Beyer, Peacock and Co. Ltd became a dormant company. The name was resurrected in the 1990s as a trading name, based in Devon.