The British Rail Mark 4 is a class of passenger carriages built for use in InterCity 225 sets on the East Coast Main Line between King's Cross, Leeds and Edinburgh.

[2][3][4] They were operated by London North Eastern Railway and its predecessors in 30 fixed formations of nine carriages, with a Class 91 locomotive and Driving Van Trailer.

Body shells were built by British Rail Engineering Limited (BREL) and Società Italiana Ernesto Breda.

[9] Disabled access was another priority of the design, so the door vestibules were enlarged to allow a larger turning circle for a wheelchair.

The Mark 4 has gained widespread praise for its exceptional crashworthiness, something that was proven in the Hatfield and Selby crashes, where experts identified the integral construction of the vehicles as being a key factor in restricting the death toll.

[15] In February 2016, a refurbishment programme called Plush Tush commenced with new seat covers, carpets and purple mood lighting in First Class.

Virgin Trains East Coast were to retain seven or eight nine-carriage sets to operate extra services to Edinburgh.

[22] Twelve Mark 4 carriages were refurbished for use by Transport for Wales on an expanded Holyhead to Cardiff Premier Service from June 2021.

[27] This plan was scrapped in favour of using newly procured Class 802 bi-mode units from Hitachi, though this never materialised as the Department for Transport ruled against Grand Union's proposal.