Thank all - much appreciated:)
Is there an easily accessible manufacturer? I assume you added more levels yourself, but the base seems solid.
Yes, indeed: IKEA
It’s made from two LACK coffee tables which I discovered when looking for something else.

The finished unit uses 2 table tops (the extra one is for the base) plus 4 of IKEA’s wheels. It also uses two of the legs from the second unit as supports for the extra shelves.
Though it’s more than robust enough in use, be mindful that the cheaper IKEA units (such as this) do not have a solid core: this one has corrugated cardboard centres albeit with wood at its structural points.
I’ll be honest that it was perhaps quite ‘lazy’ to make the storage unit in this way but the speed and simplicity appealed to me as I had so much else on my To Do list.
Here it is before the extra shelves were added, in which case it could take 6 of the 120x60 foam panels (note that the panels are slightly longer than the unit but that doesn’t bother me).

And with the extra shelves fitted:

As I didn’t want to drill through the table top, the central posts are merely glued at top and bottom.