This applies to pedestrians at level crossings:
34
Railway level crossings. You MUST NOT cross or pass a stop line when the red lights show, (including a red pedestrian figure). Also do not cross if an alarm is sounding or the barriers are being lowered.The tone of the alarm may change if another train is approaching. If there are no lights, alarms or barriers, stop, look both ways and listen before crossing. A tactile surface comprising rounded bars running across the direction of pedestrian travel may be installed on the footpath approaching a level crossing to warn visually impaired people of its presence. The tactile surface should extend across the full width of the footway and should be located at an appropriate distance from the barrier or projected line of the barrier.
Law TSRGD, reg 52
So as the HC states that the flashing reds also apply to airfields, etc, it would seem logical to apply the same status as described above (at least the first sentence).
Mister B