A little more research and I discovered that the BMW Dixi is actually a license produced version of the Austin 7. There are loads of Austin 7 diecasts out there and I have managed to pick up on ebay cheap the Models of Yesteryear 3 car boxed set.
Pictures show several different Dixi variants in use - some with the sloping speedster rear end, some with the blunt square end and some with a boot. Doors and windscreens seem optional. The only definite fixture seems to be the spare wheel fitted on the left hand side.
All I need now is a little conversion work and some seated germans in 28mm as crew. Any ideas where I could get some from?