GWR liveried TF 41146 at Cardiff Central in October 2016. © Geof Sheppard
The Mk3 coaches were devised by British Rail in response to growing competition from airlines and cars. The production coaches entered service in the mid 1970s and were able to operate at speeds of up to 125mph, a variant was also produced for use as part of HST (High Speed Train) sets. The coaches proved highly reliable and popular with passengers when in use and most of the surviving fleet are still in revenue earning service to this day.
(Information provided by Wikipedia)