Bonhams auctioneers believe they have identified the most important vase of its kind in the world.
Luxury Roman cameo vases are thought to have been produced over just a couple of generations, around the transition from first century BC to first century AD, by craftsmen of the very highest skill.
They were created by overlaying a cobalt-blue glass base with white glass. Once the hot glass had been shaped and cooled, the outer layer was then cut back to leave white glass figures.
This vase is one of only 16 now known to exist. More importantly, it appears to be a more spectacular example than the British Museum's Portland vase.
The latter stands 24cm tall, compared to the new discovery's 33.5cm, and depicts seven figures as compared to 30. The Portland vase is also missing its base.
"It is of major international importance," said Chantelle Rountree, head of antiquities at Bonhams.
"Academically and artistically it is priceless. Scholars will be evaluating this find for decades."
The vase was shown to some of the world's greatest glass experts at a Greek conference last month to great excitement - and it's hoped that much more light will be shed on its history.