A championship is a calendar of races where points are earned and an eventual champion is crowned.
A series is an number of standalone events, where there are race winners, but no points, and no champion.
A series can seek championship status if it chooses to, and are prepared to pay the championship fee to the MSA. Its a nominal amount for most club series, more if they have a title sponsor, but still affordable. The big series gets a bit more expensive. Championship fees range from £ 54 to £ 8,450, for Grade D to Grade A events
A British Championships approved by MSA
B Principal Commercial Championships
C Sponsored (and/or Commercial) Championships
D Unsponsored (non-Commercial) Championships
The MSA will award championship status to a series that has demonstrated sufficient average grid numbers over a set period of time. If a championship performs poorly they can revoke championship status and it would return to a series, but will usually issue a yellow warning card before the red card. The blue book says an average of 16 starters, but the MSA use a bit of common sense from time to time.
A brand new event can apply for championship status if they are prepared to lodge a heavy commitment deposit - £ 5000 - £ 25000
Most of the information is buried in the blue book.