This is the Hornby OO Scale Railroad BR 20T BRake Van [R60351]

Brake vans were an essential fixture on freight trains where the continuous brake was not available. Loose-coupled wagons only had hand-operated ‘sprag’ brakes which had to be applied individually, for example, before descending a gradient. 

Trains were prone to broken coupling chains, so the brake van was essential for bringing a train to a halt under such circumstances. From 1968, the requirement for a brake van to be coupled to a fitted train (wagons with vacuum brakes) was removed from the rule book. BR adopted the LNER ‘Toad D’ van as the basis for its own standard brake van design. 

This OO gauge model van is an example of a BR 20T Brake Van.