British Rail Class 315
They were built by British Rail Engineering Limited at Holgate Road carriage works from 1980 to 1981 , and they were the fifth and final variant 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 ) . 
<triplet> Holgate Road carriage works <subj> British Rail Engineering Limited <obj> operator