Zooming into that plate, I can make out "Vickers Armstrongs", "Equip MK II" "Pattern" "Rear Axle" "Reg No 4431"
Vickers Armstrongs seems to mostly have made tanks, but they also have a few anti-aircraft guns. Could this be a towable base for an anti-aircraft or anti-tank gun? The round ring in the centre sure looks like a swivel base.
Whatever it is, it's sure built solidly.
(Edit) Beaten to it. I type too slowly.