On January 2016 van insurance groups changed from 20 groups to 30 groups and the numbering system changed at the same time.
All vans registered before January 2016 had their van insurance groups numbered from group 1 to group 20 where group 1 was cheap to insure and group 20 was the most expensive to insure.
All vans registered on or after January 2016 had their van insurance groups numbered from group 21 to group 50 where group 21 is the cheapest to insure and group 50 is the most expensive to insure.