Built by the Birmingham Railway Carriage & Wagon Co in 1957/1958, all thirteen Class 104 vehicles preserved are owned by the same two private owners, who saved 12 vehicles in a bulk bid from British Rail who had a puzzling reluctance to sell a single 3-car set.
A thirteenth vehicle joined following an extended period in departmental service. In preservation, the Llangollen Railway successfully returned a power twin set to service in 1993, with a second set restored by the Churnet Valley Railway in 2004. This set moved to the East Lancashire Railway in 2014. A third set operated at the Telford Steam Railway between 1999 & 2004 but has only been used as hauled coaching stock since.