I came back from the boat moving odyssey to find a thread in full flood on Canalworld regarding old photos and obscure locations, which led to these two photos on Flickr.
It didn't take long to establish that these are indeed pictures of Chertsey in Birmingham - albeit both the place and date are not quite right. The place is nearer Old Turn than Gas Street, and apparently Chertsey was kept here for a while before being moved to Les Allen's yard at Oldbury where she remained until 2009. The date is not 1970s, but some time after 1980 - how could I tell this from the photo?
(CWF readers are, I'm afraid, ineligible to enter, as I have already given the answer away there.)