England Athletics define the rules of competition for athletics clubs generally and running clubs in particular.  Most, but not all, road races in England are run under the England Athletics rules.  Don’t argue, it is just a fact of life.
Under the rules an athlete may compete for up to two clubs.  One of these is known as the First Claim Club and the other optional club is the Second Claim Club.  Only the athlete’s First Claim Club can pay the athlete’s affiliation fee to England Athletics.
You can only have a Second Claim Club if you are affiliated by your First Claim Club.  More on that later.
If you compete in a race in which your First and Second Claim Clubs are in contention then you must represent your First Claim Club.  If the competition does not offer a team prize then you may compete for either club.
This is most important for the Interclub and Cross Country races where there are team prizes but may affect other events.
England Athletics allow a period of 12 months grace from the date your affiliation lapses in the hope your First Claim Club will renew your affiliation.  After this time they will remove your record from both your First and Second Claim Club’s England Athletics Club Portal.