Rolf,
Have a look at this picture:
and compare the snow chains(?) on this Humber Mk.4 with the one you pictured.
Source:
http://www.britishpathe.com/, still from 2143.15 | INVASION SCENES - EUROPE (ref.
missing-lynx.com > Discussion Groups > Allied WWII > Brit stuff in snowy landscape (6 pics))
Regards,
Hanno