British Railways' plans to eliminate steam hauled services on local routes led to the ordering of 4,600 railcars. As a result the railway's own workshops could not cope and a number of designs were bought in from outside contractors.
One of these was the Birmingham Railway Carriage and Wagon Co. which came up with this distinctive design based round the standard BR specification, and using the same windows and body profile as a standard Mark One coach.
M50447 was built in 1957 to lot number 30293 as part of a three-car set for the London
Midland Region. It has two Leyland 680 engines and its body design is based on that for a Mark 1 coach.

Originally painted plain dark green this vehicle later acquired the distinctive "speed whiskers" which were then superseded by the yellow warning panel, covering half of the vehicle end. In later years it was painted blue with an all-yellow end and it was in this livery that it was delivered to Llangollen. It was painted (on one side only!) BR green when stabled at Glyndyfrdwy and remains in this scheme today. 

50447 was delivered to the London Midland Region in September 1957 and was originally part of a set with 59155 (a centre trailer)  and 50499 ( a driving motor composite) originally allocated to 5B (Crewe South). By 1959 it was at 5D (Stoke) and moved on to 16C (Derby) by 1967. Later in its life it moved on to 9L (Buxton), by this time numbered 53447 to avoid confusion with new locomotives being built in the 50XXX series. Withdrawn in 1993 it was purchased for preservation for use as spares but survived largely intact in use as a headquarters for the Llangollen DMU Group (which later became Llangollen Railcars). Although currently still in use as a mess coach/heaquarters and stabled at Pentreflin Sidings the vehicle is considered to be in restorable condition and this has now been stated as a long-term aim.