Part of the problem is the contract. As the OP signed it, unless there is yards of it in an exceedingly small font, I bet German law is that he agreed with it and the terms and conditions etc. The relatively small point of a miles per hour speedo in a German market car would be cheaply rectified by its replacement with a kilometer unit.

However, and this is something I have no idea about, are there any any other differences in specifications? The steering wheel and speedo suggest a UK market car, does the German one differ in other respects? Given the EU probably not, but ought to be checked as anything that says this is not a car for Germany will help.

While I'd normally suggest taking a matter in the first instance to the dealer, I think the OP needs to speak to a solicitor and see where he stands.

1930 Super Sports Aero 'The Elk'