The receiver was the issue - replaced that and now it all works, barring a slight mishap with the transmitter having mixing enabled at the same time as the ESC but it is back together. The axe has been lightened and now definitely seems to fire much quicker. The motor wiring I resolved by making up some Y connectors so that it is much easier to wire the motors to the ESC.

Now it is a case of charging the batteries and seeing how it runs.