In order to race in British Cycling events, you'll need a race licence and to get that you need to be a member of British Cycling.
If it's your first year, get a £20 discount here. (Promo code: NEWCMRA)
Bronze: Provisional licence. This is enough for most BMX, MTB or Cyclocross races, however road or circuit races still require you to pay additional £5/race.
Silver/Gold: Required in order to buy a Full Race licence (extra £35). This allows you to earn points for yourself and the club. More info here.
Options for Insurance
CTC Membership (£18): 3rd Party insurance cover and legal support (on/off-road, inc. sportives and time trialing). Other perks listed here.
BC Silver (£40 or £20 1st year): Liability insurance (inc. racing) and Legal support (inc. racing)
BC Gold(£69 or £49 1st year): Personal accident insurance and Enhanced bike insurance discount.