british rail class 507 electric multiple units were built by brel at york works from 1978 to 1979. they were the third variety of british rail's then-standard 1972 design for suburban emus, which eventually encompassed 755 vehicles and five classes (class 313/314/315/507/508). the 507s were the first variant to be 750v dc third rail only. they have worked on the merseyrail network from new, and continue to do so, now refurbished by alstom's eastleigh works.