Hi Jason, absolute correct in your comments as usual!!
Its a St Pancras Iron works wagon of the later period of manufacture, 1905 onwards. There are some pictures of the early wagon with Artillery ( wood cart type wheels) in the Chubb locks archives. These wheels are cast steel I believe by Krups … Mr Chubb had a business interest in the St Pancras wagons company so used them for advertising with his safe boxes as load.One was sold to the NER railway I believe…yes steel tyres on slippery cobble / mud roads would not have been good driving…
regards vic