Thanks Paul.
Kevin, I said I would provide a little more info when I arrived home so here goes. These are an incredibly well made and robust unit, with strong cast wheels without being too heavy for practical use. Our hoe has a brass plate riveted to the left handle which reads:
PATENTED DUPLEX DISC HOE. PAT NO 567891. SUPPLIED BY CENTRAL GARAGE, REDDISH, STOCKPORT. No A/1927. MADE UNDER LICENCE BY HAYES ENG Co Ltd, SPEKE, LIVERPOOL.
All the duplex hoes I have seen have either the brass plate with this information on or the evidence that such a plate had existed.
I have never seen any literature on this product, does anyone have anything?
Ours is mid/dark blue with red wheels and I have also seen mid/dark green with red wheels.