From the AAIB report:
The helicopter remained upright and the commander shut it down in the usual manner, except that he waited for the rotor blades to stop before turning off the electrics, as the rotor brake is inoperative without a weight-on-wheels signal from the landing gear squat switch.
The only thing that operates is the (rotor brake) light on your instrument panel. In short: No wheels, no rotor brake.