The original Tri-ang model of the Class 31 had sold in many thousands over the years and earned Rovex a lot of money in the process. Towards the end of production the tool had become very worn, this could particularly be seen in the misshapen windows which had become rounded. When it was decided to replace it in 1976, thought was given to what would be a suitable replacement and a Class 50 was suggested. This, however, was not followed through and, instead, a Class 25 was eventually chosen.

Twenty years later Hornby were offered the tools to the former Airfix Class 31 diesel and it seems they were turned down because they duplicated a model already in the tool store. Possibly by then staff had forgotten how bad the old tooling was. Another eight years after that Hornby were producing a super quality model of the Class 31 and that is the one that is in the catalogue today.