The simple fact is there is no real public appetite for Police helicopters (unlike HEMS).
Ask most people what they think and the majority will just moan about the noise/privacy concerns/constantly flying over my house etc
When it comes to public money, people would rather see it spent on more "worthy" things than "toys for boys".
Just read the comments under this article:
The real flying squad: on patrol with London's chopper coppers | UK news | The Guardian