Well I would never have guessed that, well spotted Chris.
There’s some 1926 adverts in the gallery with a 22″ cut water cooled mower.
http://vhgmc.co.uk/photo-galleries/governor-john-shaw-and-sons/

Also I have a couple of 1924 adverts but they do appear to be of a different model to the one Geoff has photos of. Note that they have the same roller though.
From a bit of research I did a while ago many UK produced machines were exported to Australia.