The armoured vehicles, depending on the type of spec, would quite dramatically change the dynamics of the vehicle. For example the Rover 827 armed response cars used in many Police forces commonly featured reinforcement in the bulkhead, doors and front glazing (the glass was not strictly speaking bullet proof but could withstand small-arms fire), with uprated suspensions and brakes to try and cope with the weight at the front end. Even then they were understeery monsters that could easily shaft a set of discs and pads in under 10k if they were busy. Certainly they just couldn't be driven as fast as a standard plodmobile as contrary to myth many weren't modified beyond Rover tweaking the ECU to get a few more horses, the Honda unit was complex enough as it was and the Japanese didn't like their products being modified in anyway without their permission. Which could take months sometimes.
A few years back I was shown round the specialist glass makers involved in producing ballistics- resistent screens. The laminate substrate is (or was back then anyway) a restricted product in the UK available only on licence with approval by the MoD. Very, very clever stuff, although the thickness and therefore weight of the finished laminated glass was frightening, but the firms involved were exceptionally good at hiding the obvious difference. An example I saw was a screen for a Bentley and you had to looks closely before you saw it was nearly 100mm thick.
You're not wrong Blue. 
The first general issue vehicles had linear ballistic glass carried in a frame behind the windscreen, behind that was a sheet of clear acrylic designed to prevent the spall from bullet strikes on the ballistic glass entering the cabin posing a threat to the vision of the crew.
Door windows were sealed in the up position again with acrylic sheet between them and the interior of the vehicle, so the only ventilation was from aftermarket air conditioners. (Viking make, if I remember)
If you haven't driven an armoured Landcrab or Mk4 Cortina - you haven't lived. 
Furthermore, to see bullet strikes on ballistic glass - from the inside - is quite a sobering experience.
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The latest armour is light-years ahead of what was, although driving these vehicles is a specialised task and remains a bit of a pain in the arse to tell you the truth.
I remember reading an article some years ago about an armoured Rover P6B used for the Queen? PM? anyway it was gas tight and had it's own oxygen system if needed. The front screen was so thick that a smaller steering wheel had to be fitted....

The car was, and I believe still is, registered as an operational Police Car in a Met Museum.....

Article was in 'Practical Classic Magazine' some years ago...
