Motor Rail was a British locomotive-building company, based in Bedford, England. Formed in 1911 as The Motor Rail & Tramcar Co Ltd, they built Petrol and Diesel engined locomotives, mainly narrow gauge. During World War I over 900 locos were supplied for use on temporary military supply railways. The trade name Simplex was used from the early days; in 1972 the company was renamed Simplex Mechanical Handling Ltd.
For further and more detailed information see Wikipedia at Motor Rail]