For BC events, if you need at least a provisional licence and you'll have to pay a £10 day licence fee to ride closed circuit races (in addition to the entry fee). You won't be able to ride road races. If you're planning on doing regular racing it pays to take out a full licence (wider variety of events and cheaper in the long run).
I would add that if you're not interested in getting points then there seems little point getting involved in races, 4th cat races can be pretty twitchy and the aim is to get your points and move on.