Here is something very similar with the mark "Schott Zwiesel" on the bottom. Just a thought, a direction to look in.
Hej Ivo - Thanks for the hint, could be related, but have made a search in "Schott Zwiesel" items without any luck, but I will have it in mind for the future.
Christel Holmgren-Exner have also made for Holmegaard Glasswork a design from 1967 with heavy base in the Kvadrille serie
The glasses could also be of Danish or German origion, although I doubt that they are Danish, I would think I would have notice, but on the other hand, we have several small glass studioes in dk.