If I remember correctly, and I can't find a reference off hand, commercial
vehicles of over 3500kg and pre 1960 are exempt from needing an MoT. You are
not allowed to carry a load however. Its all to do with them not fitting on
a standard MoT testers ramp and so having to be done (or not done in this
case) by HGV testers.

I suppose this one could just slide in.

A friend has a pre-war 3 tonner and it certainly does not need an MoT.

Malcolm