The 20 point rating system is quite extended around Europe. It’s employed,

The 20 point rating system is quite extended around Europe. It’s employed, among others, by the ’Vinum’ magazine (with editions in Germany, Switzerland, France and Spain), elmundovino.com (from El Mundo, a Spanish newspaper) or ’The Vine’, the newsletter written by Clive Coates. In all these publications a 12 out of 20 seems to be equivalent to an 80 point wine rated on the WA or WS.

I can’t found that comment from Jancis that the ";great majority"; of wines she tastes are scored somewhere between 15 and 18.5. Anyway, I think this is the result of her bias (as with most wine critics) towards tasting the best wines on the market.