When you transfering BC to CCRB, you are transferring amount worth of Beecoins. For example, if you transfer amount (£) worth 50, you have converted £50 worth of beecoins to CCRB. So the approx. calculation will be  50 x 1.2339* / 3.99** = 15.4624. Which means you will be able to transfer approx 15 number of Bee coins to CCRB. 

* Approx. Sterling pound to USD value.

** Internal value of Beecoin.