I haven't got my old manual to hand at the moment to look up the
precise wording of the instructions. The main exemptions from the Road
Traffic Act that emergency vehicles can claim are to treat red traffic
lights as give way signs, and to exceed the speed limit. Its worded
something like where to obey them would hinder the vehicle in its
duties. I don't think there is any actual mention of the use of lights
and sirens as such, apart from a secondary exemption is the ability to
use audible warnings at night. Individual services (and even
preferences from one instructor to another) will have their own
guidelines.

The bottom line is, if you are claiming any exemption (eg speeding),
then you could end up in court explaining both the reason why ("I was
attending an emergency call"), and what means you were using to warn
the public ("I had the blue lights and sirens on"). So although having
the siren turned off, as you take out a pedestrian who steps out in
front of you, wouldn't be in breach of any law as such, it probably
would count towards your dangerous driving sentence.

Consequently, any time the siren is turned off while attending an
emergency call, the driver is to some extent putting other road users
and his driving licence at risk. People will always come from nowhere.
There will always be pedestrians who step off the kerb without looking
and people who suddenly pull out of side turnings without looking.

There has to be an element of common sense and as I said I and nearly
all of my colleagues tended to turn the siren off if there was no
visable hazard. But that was the risk we took. I wouldn't criticise
anyone for taking the other option and leaving the siren on from
station to scene. You only need a kid to run out from a shop across the
road and the first question we'd be asked was whether the siren was
turned on.

I'm not at all taking issue with your post (you weren't being
confrontational at all!) but any potential hazard is a hazard whether
obvious or not. People by the side of the road might step out whether
they look like they might or not, and unless they are well away from
kerb would really need the siren to be sounded. Any junction whatever
the priority is also to some extent a hazard. There has to be some
common sense, but ultimately as I said any time the siren is turned off
there is a risk (probably to the drivers licence and career more than
to the public - I'm well aware sirens can also be disorienting to the
public at times). I am sure having the siren turned off would always
count against you in court.

As for the vehicles with the sirens off when they should more obviously
be turned on, there is a need for silent approach sometimes, but
obviously extra care must be taken. Certainly from a paramedics point
of view, with a patient on board we would try to keep the siren use to
a minimum (although taking a patient in with blue lights going is
relatively rare anyway) because of the stress to a conscious patient.

I'm not trying to excuse bad driving on the part of emergency staff,
obviously as in any job some people are more competent than others, but
I do feel that the majority (not all) of the criticism they get is
completely unjustified.

As for how you stand going through a red light to make way for a fire
engine, I dunno! I like to think that it would be taking into
account.....