What's the general stand point on advance warning beacons in this type of scenario (if indeed there is one)? By that, I mean a sign is accompanied by flashing lanterns, active while the signals are red. They seem to be common elsewhere in the world, but they don't seem to be common here at all.
I can only think of one set (M56 J12 E/B Exit) that are now gone, they used to flash when the signals were in use.
Not directly a signal warning, but there used to be big fibre-optic queue warnings on the A5036 and A59 as they crossed the Leeds Liverpool Canal outbound because of 'hidden' signals, though these were removed many years ago and not replaced. More recently, an LED one has appeared on the A59 in roughly the same place, that I think activates when the signals change to red, but generally speaking this scenario is more readily fixed with high-level signals.