On the Police car front, he/she is indeed allowed to do what ever speed he/she feels is appropriate, BUT if they have an accident it is generally considered as their fault.
I only have experience of the London Air Ambulance, and I know that they have a set limit on the amount of space that they must have to land. There was a case, I believe, of a pilot being suspended from their crew for landing in a too small an area. Contravening procedures and all that.
The chief chappy that suspended him, then prodceded, the following week, to try and take off from the roof of the hospital with one engine at flight and the other at ground idle. Following this incident, he then suspended himself!!!!! <img src="smile.gif" border="0"> <img src="confused.gif" border="0"> <img src="eek.gif" border="0"> Luckily the co-pilot was on the ball and realised what was happening.
All very strange, and that was told to me third hand, so any discrepancies, I apologise now.
"Some days you are the pigeon, some days you are the statue!"