Too fast, the number plate cannot be read.

It's unlikely to have been a police car, even unmarked, the lights would have been blue.

My Dad tells this terrifying story from a number of years ago when as a truck driver he was heading from Inverness to Elgin. As anyone who has been on this stretch of (single carriageway) road will know, there are a few very long straight sections. He could see some distance away heading towards him, another truck, but this truck was on the wrong side of the road. It got closer and closer and he was getting more and more alarmed. At pretty much the last minute he had to make a split second decision to go to the wrong side of the road to pass the other truck. As the trucks goet close enough he could see the other driver was either asleep or unconscious slumped to the side, so he blasted his airhorn as he passed and in his mirror, saw the truck veering wildly for a few seconds before straightening up on the correct side of the road. So the driver had been asleep!. Fortunately no other vehicles were involved, but it could just have easily resulted in a very serious accident.

An emergency call out for a doctor or senior fire brigade person? Some of them use umarked cars with discrete flashing lights.

The rules for lights on emergency vehicles are quite closely legislated (though my experience may be a bit out of date).

Generally, the vehicle must be being used for fire, ambulance or police purposes but there are others, such as Mine Rescue, etc.

AFAIK, lights to the front can be any colour except red, lights to the rear can only be red, blue or amber.

When I was working, my car had blue grille lights, alternating main beams and a 'Kojack' magnetic roof beacon (these fell out of favour because they had a tendency to fall off at high speed).

Because of controls nowadays, if this was a police, fire or ambulance car this would be checkable via the authority concerned.

I think this is quite an important point. Whilst drivers of ESVs do have some latitude to disregard speed limits, road signs, red lights, etc., all of their training and all professional dictats are that they must always drive with due care and attention, not recklessly or dangerously. 'Blues and twos' do not give you immunity from anything. The best police driving instructor I ever had taught us to drive fast without using them.

There are occasions when police driving can seem to be dangerous when it really isn't - for example in a high speed convoy has a 'pilot' car or motorcycle that is reporting back that blind bends etc. are clear of traffic. But in all circumstances, ESV drivers have exactly the same duty to drive safely as anyone else.

As I understand it, nowadays vehicles responding to calls are closely monitored by their control rooms, so that a fast response is authorised or not. Not a bad thing, IMHO.