Answering my own question - I think it must be the same man. In 1919 a Canadian Major H R Northover (obviously he got higher than Captain) won the Silver cross of the British National Rifle Association at Bisley. There is still a Major Northover competition at Bisley to this day. In 1938 the same guy won a major (no pun intended) UK clay pigeon shooting competition. The enclosed link takes one to a photo of the man himself
http://www.scienceandsociety.co.uk/r...g=3&imagepos=2
Just look at all those shooting medals. The archives of the TUC in 1948 contain a paper written by Hugh Dalton (Chancelor of the Exchequer in the Atlee government) giving recollections of Major H R Northover who is described as a gunnery expert (unfortunately there is no online access to this).
I'd definitely like to find a shot of the bike in question.