achrn,
Constructing a go-cart doesn't exactly slot into the interpretation (Reg 2)!
extract from the Regs:
Construction work includes -
(c) the assembly on site of prefabricated elements to form a structure or the disassembly on site of prefabricated elements which, immediately before such disassembly, formed a structure.
Structure means -
(a) any building, timber, masonry, metal or reinforced concrete structure, railway line or siding, tramway line, dock, harbour, inland navigation, tunnel, shaft, bridge, viaduct, waterworks, reservoir, pipe or pipe-line,
cable, aqueduct, sewer, sewage works, gasholder, road, airfield, sea defence works, river works, drainage works, earthworks, lagoon, dam, wall, caisson, mast, tower, pylon, underground tank, earth retaining
structure or structure designed to preserve or alter any natural feature, fixed plant and any structure similar to the foregoing.
Looking at your attached links, it seems clear to me.