"Cold Zero" By Chris Whitcomb has made it here in the UK and it's fantastic. Covers Ruby Ridge, Wacco etc. I must for any LEO.
I have read loads of books re Delta, SAS(not BravoTwoZero - its ****), SBS etc, but the best British police biography has to be by Steve Collins called "The good guys wear black." He was in the British equivilant of the countrys top SWAT unit.
Another good one is "Trojan Files" by Roger Gray. It explains famous shooting events in the UK, and how much BS British LEOs face, regarding being deployed with firearms.
Both are available at Amazon.