Welcome, Kilcock!
Little worms in yellow and black rugby jerseys, roaming around in a big scrum? Those would be grape leaf skeletonizers. There are a couple of organic sprays that I would recommend here, but I understand they aren't available in Europe. They can be sprayed with a solution of organic dish soap, but that only kills the ones it directly touches--you have to be very thorough with it. The only other organic control is to pick off the leaves with "scrums" on them, and stomp on them. Carbaryl and the synthetic pyrethroids are effective, but more toxic to children pets and wildlife. Hope that helps some!