2014 KIMC keystage3-IWYMIC individual Question 14

In triangle $ABC$, $\angle ABC=\angle ACB=30^\circ$. $O$ is a point such that $OA=OC=1$ cm and $OB=2$ cm. Moreover, $\angle CAB=\angle CAO+\angle OAB$. What is the length, in cm, of $BC$?