You can use whostheref to set your availability. Be available if you want to referee. Don't be available if you cannot. 

The official site to look up the laws of the game

The official place to look up rules and regulations from the RFU. This is particularly useful to find the Age Grade rugby appendixes. 

This is the RFU page promoting concussion awareness and education. There are many useful resources available to download here. 

The EMRU pages contain useful information such as the rules and regulations for junior rugby competitions and merit tables. Affiliated clubs, CB and sub-county details can be found here.

The Midlands Division pages contain useful information such as the rules and regulations for knock out competitions.