New group structure as hinted in the webinar here:
https://www.bbc.co.uk/sport/cricket/articles/cy7y5y2z46ro"Men's Vitality T20 Blast
The group stage of the Vitality T20 Blast reverts to three groups with North, Central and South Groups with the eight best-placed teams on points and net run-rates going through to the quarter-finals.
North Group: Nottinghamshire, Derbyshire, Lancashire, Durham, Yorkshire and Leicestershire
Central Group: Gloucestershire, Northamptonshire, Birmingham, Somerset, Glamorgan, Worcestershire
South Group: Surrey, Sussex, Kent, Middlesex, Essex, Hampshire
Each county plays the other teams in their group home and away - a total of 10 matches.
They will additionally play one home game against a county from outside their group and one away game against a side from another group.
The top two teams in each group plus the best two third-placed teams progress to the quarter-finals. The winners of the quarter-finals will progress to men's T20 Blast Finals Day."