Flashing Red lights are an absolute stop in law. Whereas steady Red lights just mean stop.
What's the difference you may ask?
Well an absolute stop means you must absolutely stop. For example, emergency services can treat a stop red light as a give-way sign when responding to an emergency call, but they must stop at an absolute stop red light. Yes - that means that even the police/fire/ambulance have no legal defence for jumping the red lights at level crossings (or other places they exist, such as lifting bridges).
I saw an example of that last night at Wokingham Station.
At about 0:25, I glanced out of the window and saw lots of blue lights flashing. An emergency ambulance was waiting at the crossing, which had its barriers up and wigwags on. It waited for half a minute or so, then crossed. Immediately afterwards the barriers came down and a train quickly arrived (5C86
ECS▸ to Reading to Staines, so not stopping at Wokingham).
So what was going on? Did the ambulance driver ask for clearance to cross, and wait for confirmation? I imagine they would probably use radio to their control, but might have got out to wave and shout to the signaller (it's too far for me to see that).