A supermarket chain in Germany has denied deliberately using neo-Nazi codes in a Christmas advert - but an expert on the far right said she believed it was no accident.

Sabine Bamberger-Stemmann, director of the Regional Centre for Political Education in Hamburg, told Germany's Manager magazine that the Edeka ad showed two car number plates that displayed common codes used by right-wing extremists.

According to Ms Bamberger-Stemmann, it was highly unlikely that the number plate stamped with "MU SS 420" appeared by accident because the letters SS - short for Nazi paramilitary Schutzstaffel - are not permitted for use on German cars. In addition, the number 420 is an abbreviation for Hitler's birthday, which was April 20.

Ms Bamberger-Stemmann added a second plate contained further number combinations that were familiar on the far-right extremist scene.

Hamburg-based Edeka corporation, one of Germany's largest supermarket chains, said the number plates were fake and an entirely benign message had been intended.

A spokesman said they regretted the impression created by the advert.

But Ms Bamberger-Stemmann did not accept the explanation. These codes "are easy to research in the internet," she said. "Ads for right-wing radical products and ideas often use these codes. To see them [here] is upsetting."