Looking at the Sectional Appendix, London Road Level Crossing marks the boundary between two Tokenless Block sections.
For passenger trains terminating at Bicester Town from the Oxford direction the Driver contacts the Signaller at Oxford on arrival and when ready to depart.
For through trains:
There are two signals at the crossing (BT100 and BT200), each with a control cupboard. Before operating the crossing, the Guard indicates the train is complete and then requests access to the next block. Assuming it's given, the Guard initiates the crossing sequence.
Once the barriers are proved lowered, the signal should clear, at which point the Guard locks the cupboard and rejoins the train. The barriers automatically raise once the train has cleared the crossing, and there's an indicator 1/4 of a mile further on to confirm that.
If the indicator fails to illuminate, the Guard has to walk back and check, then try raising the barriers with the raise button in the control cabinet, and if that doesn't work, the barriers have to be raised manually.