Flashing your vehicle headlights a couple of times will make the traffic lights change to green.
Rationale is that the traffic signals can somehow detect the flashing lights of blue light services and give them green.
This technically isn't a misapprehension - just misapplication
Torquest market a system called opticom - invented and marketed for a long while by 3M - which uses coded IR emitters to trigger traffic signals for emergency vehicles or where there is tram / bus prioritisation - not aware of UK 999 service use
however some UK emergency services, fire services in particulsr have a system to provide a green wave on certain road 'corridors' out from stations - although at quiet times in a fire appliance or if you try to use the system in a police car , ambulance FRV or a full sized ambulance working from the same station / site you'll often get 'ahead' of the green wave ...