This is the W.5511 "Milk Marketing Board" 6 Wheeled Tanker Wagon in Black  with standard Wrenn white metal chassis and the later Wrenn, Cheshunt wheels. Issued in the early years of Wrenn, Cheshunt production. This differs from the Wrenn, Basildon prototype in my collection as it is sprayed black on the plastic body.

This is No 87 of 100 issued during the Wrenn, Cheshunt years, and is becoming RARE to find today