Alexander George Thornton may have begun his career in the drawing material trade by becoming apprenticed to W. H. Harling of London. Between 1874 and 1878, Thornton worked for George Gallie & Sons, booksellers and stationers of Glasgow. In 1878, he set up a business in Manchester at 8, Albert Square in partnership with Joseph Halden as wholesale drawing material importers and mounted paper manufacturers. However, this partnership only lasted for a couple of years and Thornton moved to premises of his own at 109, Deansgate. By the 1890s, these consisted of a single-fronted shop with show rooms, warehouses, and workshops at the rear and in the basement.

The firm soon built up a large national trade and an extensive export business to all parts of the world. It did a special line in loose drawing instruments which it claimed were the cheapest for their type and quality ever offered. It also introduced a case of drawing instruments in 1892, which provided good, reliable instruments at a 'convenient price for students and apprentices'. The company introduced a number of improvements to instruments and equipment such as drawing boards. By 1895, new designs included rotating compasses, screws for drawing instruments, a miner's dial, fluid transfer ink for drawings or tracings which were to be copied, a typograph copier and a paper stretching board.

In 1897, the firm moved to 11, St. Mary Street with works on Bridge Street and, again in 1904, to Paragon Works on King Street West. Here there were showrooms, main offices and warehouses, and facilities for mounting hand-made papers and maps. Manufacture of surveying, drawing and other scientific instruments took place at the Minerva Works on Sidney Street, Salford, purchased in 1907.

During the late 1910s and 1920s, the business expanded quite rapidly due to the growth in demand from colonial and other overseas markets. In 1912, larger works were acquired in Cross Street off Lloyd Street in Hulme. The works moved again twelve years later to be split between two premises in Heald Place, Rusholme and North George Street, Salford. The company also patented several of its own designs of drawing instruments such as beam compasses, drawing curves and dividers. It used international exhibitions to advertise its products and won medals at the Franco-British Exhibition, London, in 1908 and at the International Exhibition in Dunedin, New Zealand, in 1925-6. By this time, Thornton’s customers included leading universities and colleges and government departments around the world. During the 1920s, production costs for hand-made drawing instruments increased. Companies, including A. G. Thornton Ltd., introduced more machine-made instruments using standardised and interchangeable parts. The King Street West premises were destroyed during the Second World War and the various departments were dispersed to different parts of the city: the offices to Gartside Street, export department to Brazenose Street and showrooms to Bridge Street.

In 1949, the company moved to purpose-built premises in the new industrial park on Longley Lane in Northenden. The retail showroom was retained on Bridge Street in the city centre. A special feature of the new building in Northenden was its dust extraction system to remove dust created by machinery. By this time, the company had 220 employees, most of whom had been there for many years. The managing director was

A. M. Thornton, a grandson of the founder.

In 1967 the company changed its name from A G Thornton Ltd to British Thornton before acquiring two other companies in 1992, Educational and Scientific Furniture Ltd and Armstrongs (Hull) Ltd. The company moved to Burley, became known as British Thornton Holdings Plc and became a leading supplier of educational and scientific furniture market.

After the appointment of a new Chief Executive in 1996 the company was acquired by a management buyout. British Thornton Direct Ltd became the parent company and British Thornton ESF Ltd the trading company. In 2015 the company merged with Claughtons, a Yorkshire company, to become the largest manufacturer of educational furniture in the country.