what are the rules in a fell race regards first aid

last week i was asked to cover for first aid duties tonight for our club race as st johns are charging us £80 for two of there members to attend.
our secretary has me and another member to do it
we are both qualified first aiders.

im not sure what the rules are for fell but the summer league that we run in stipulates you have to have two first aiders if your club organisers a race.

okay £80 doesnt seem a lot but last year we had a incident and honestly i thought the way the two first aiders that we bought in dealed with it wasnt good enough.

whats the rules
anyone know.