Thanks for the input folks. Taken with some other factors I think mid to late 70s would be about right for this gents frame of mine. I've made it into a sort of quasi touring bike. It used to have down tube shifters on it but they were atatched with a band rather than brazed on lugs. There is a small semi ball bearing type nodule on the down tube which was presumably for locating the band. I've put some pod type shifters on the handlebars but despite being handy they look quite wrong so will be changing back to down tube shifters soon.