Its a Vauxhall, most likely.
This was their large family car after the Vauxhall Cresta and before the Carlton. It should have a 3.3 litre in-line six, and was produced after General Motors owned both Vauxhall in England, and Opel, in Germany, so there may be some parts in common.
The styling is a bit Italian, perhaps a styling house like Bertone or Pininfarina was contracted to do some work on it. You may find more info with a search engine, but include "car" or you may get Vauxhall Bridge!
Simon.