the british rail class 317 electric multiple units were built by brel at york works in two batches, from 1981-82 and 1985-87. they were the first of several classes of british rail emu to be based on the all-steel mark 3 bodyshell, departing from the "pep"-aluminium design which had spawned the earlier class 313 to class 315. the mark 3 bodyshell was also the basis of class 318, class 455, and the diesel "sprinters" pioneered by the class 150.