David, you may be right about the classification of the chair. I have the tendency to call any large saloon sidecar a "double-adult" but my experience of the things is restricted to riding a BSA with a box of bricks on the float into a telegraph pole !
I remember the winter of 1962-3 because the snow alongside the garden path stood higher than I did.
I tend to think "Busmar" with most of this type of sidecar but there were of course many small manufacturers.
http://images.google.co.uk/imgres?im...%3Den%26sa%3DG
The small car was responsible for their demise, along with the MOT test as many were not all that well maintained.
I should think it a certainty that this rider was ex-Services, either wartime or National Service. I wonder if he was wishing he was back on a WD Big 4 Norton with sidecar wheel drive ?