The first standardised railway carriage design built by British Railways, the Mark 1 Coach introduced in 1951 continued to be produced until 1963, and even later in the form of multiple units and non-passenger stock.Mk1 Coaches were built in various places including Derby, Doncaster, Eastleigh, Swindon, Wolverton and York.tion of the Class 800 and Class 801 IEPs.