Thanks very much for the advice. I appreciate it and will give it a go.
I spent ages trying to get a decent answer from the supplier. Finally, after a rather poor response, they told me to talk to VDO as they had no idea. I think I must give out a a subliminal message over the internet which says 'please waste my time - I have nothing better to do!'
Anyway, I'm off to France at the end of the week so I'll live with it until then and sort it out when i get back.