Notes on Emergency Services:
Police
Police cars models are generally SUV's or estate cars. The Jaguar currently in-game isn't an absurd choice, though I wouldn't really call it typical. If I could pick something to replace it, I'd probably go with a
Vauxhall Astra Sports Tourer.
Policing traffic is the responsibility of territorial police forces, of which there are 43 spread between England and Wales. Scotland and Northern Ireland each have a single, national-level police force. There is no strict national standard on patrol car liveries, and they can differ between individual cars even within a single police force. As such, it's probably best to create a generic livery, and make variations of it for each of the four nations.
England/Generic
Cars are either white or a light silver, with white being more common. The front of the car typically says 'POLICE', either forwards or mirrored. The side of the car can have markings covering it in its entirety (
example), or with the bottom half left blank, sometimes with 'POLICE' written there (
example). The rear of the car also typically has 'POLICE' written in red (
example).
Usually the badge of the local territorial police force will be displayed on the sides of the car, though there are also examples where that is absent, so for a generic police car it is fine to ignore that detail.
Wales
Welsh police cars are similar to England, but are additionally bilingual, with the word 'HEDDLU' written above or alongside 'POLICE' on the
front and
rear of the car. The 'POLICE' text on the side of the car is typically absent in Wales as far as I can tell.
Scotland
Like Wales, bilingual cars are becoming more common in Scotland, with the Gaelic word 'POILEAS' written below 'POLICE' on the hood of the car (
example). The
logo of Police Scotland is also typically placed on the hood of the car above the text.
Northern Ireland
Similar to England. The logo of
Police Service Northern Ireland is featured above the 'POLICE' marking on the hood (
example 1) (
example 2).
Ambulance
Most Ambulances in the UK are based on the Mercedes-Benz Sprinter, though I can testify that Ducato/Boxer/Relay based ambulances do exist. Notes on each country:
England
There are 10 Ambulance services on mainland England,
as listed on Wikipedia. The logo and name of the services are typically listed
on the side and rear of the Ambulance. The 'EMERGENCY AMBULANCE' text on the side
and rear is common to all English Ambulances, and should be featured on a generic example.
'AMBULANCE' is typically written in reverse on the hood of the vehicle. The exception to this are London Ambulances, who instead have their logo on the hood, and 'LONDON AMBULANCE' text above the windshield (
example), as well as the rear.
Other Nations
Helpfully, the other three nations are served by a single Ambulance service each:
The Welsh Ambulance Service use vehicles with text primarily in Welsh. (
front) (
rear) (
side detail).
The Scottish Ambulance Service use white vehicles, rather than yellow (
example 1) (
example 2).
The Northern Ireland Ambulance Service use vehicles that are largely the same as those in England, just
with relevant branding.