Its a terrible junction, that I use almost every day. As Oliver says the curbline sweeps round to the left. Also the buslane on Southampton Row ends close to the junction so that cars wanting to turn left have to cut sharply out of the middle (staright ahead) lane. It can be chaotic as the cars try to reorganise themselves.
There is also no obvious way to get from Bloomsbury to Aldwych which avoids it (without a detour)