The Class 31/4's were conversions of Class 31/1's and had electric train heating (ETH) fitted and were numbered 31400 - 31469 for use on passenger services. The ETH rating of the Class 31/4's was sufficient enough to provide power to an 11-coach train although in practice the loads of Class 31/4 services rarely exceeded 5 or 6 coaches.
TOPS number range was 31400 - 31469 and were introduced into service between 1970 and 1985.