Mk4 FOD 11312 at London Kings Cross in September 2009. ©Hugh Llewelyn
British Rail's fourth design of passenger carriages was designated Mark 4, built for use in InterCity 225 sets on the East Coast Main Line between King's Cross, Leeds, Newcastle and Edinburgh. As of July 2020, 19 Mark 4s have been scrapped, 144 are still in service (formed of 16 9 carriage sets), and 139 are in storage. A small build compared with the Mark 2 and Mark 3 designs, 314 Mark 4s were built between 1989 and 1992 by Metro-Cammell's Washwood Heath factory to operate services on the newly electrified East Coast Main Line. The Mark 4 is an all-steel coach incorporating a number of improvements over the Mark 3 stock - notably the inclusion of automatic push-button operated plug-type doors, in place of manually operated slam-doors, fully sealed gangways and controlled emission toilets (CET).
(Information provided by Wikipedia)