Mordred (or more commonly known as Ferret) is a 4 Wheel petrol engined locomotive. It has a standard BMC A series petrol engine from a morris minor car linked by a gearbox to the wheels. The clutch uses standard car parts and drive to the wheels is by chain.

The engine is very unusual in having been both 2 foot gauge and 15 inch gauge. it even went for a trip on the Ravenglass & Eskdale Railway in Cumbria. It was built by Terry Stanhope from Leeds in 1969.

Mordred was the evil brother of King Arthur. The engine got this name after it stopped working at the far end of the railway and had to be pushed back 1.5 miles to Rudyard by the driver Jim Hawksworth. Used now only for works trains it was originally used on passenger trains. A video showing this has come to light.

The main improvement to the engine was the overhaul of the engineby Dave Cruikshank from Middlewich. The cab was lowered slightly, and a back fitted. The engine was then repainted in dark green and got the nickname and nameplates for the Ferret. Air brake pipes have been fitted which work on the train. The engine only has a handbrake. It has been overhauled numerous times in recent years in an effort to make the engine more reliable and was repainted into its current black livery in 2018.