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I have ben a police officer in London for 27 years and a rotary pilot for 5 years. I am not a member of the Met ASU (too tall unfortunately).
In answer to your hypothetical question, from my point of view, these aircraft are worth their weight in gold.
They have on one occasion amost certainly saved my life. Whilst chasing a suspect after a very nasty GBH robbery the chase ended up on a railway line and the chopper crew warned me to get off the line urgently as an itner-city was coming round the bend behind me.
As far as vehicle pursuits are concerned, one of the main advantages of having an aircraft above is not as most people think, to get video footage for forthcoming tv programs, but it allows the following ground units to back off whch not only reduces the danger to the police officers but encourages the bandit vehicle to slow down, thereby reducing the danger to the public.
In these days of increased terroist activity the police helicopters play a large role in making life difficult for the terrorist organisatons in ways that for obvious reasons are kept out of public awareness. I am not even privy to all of the jobs they are called upon to undertake. In fact the role of the police aircraft go far beyond what the public are generally aware and therefore an answer to your question is consequently very difficult to give.
I think it would suffice to say that I think the Air Support Units are a very effective tool for todays police services.
This thread itself oviously shows that the criminal fraternity are concerned about the presence of the aircraft which means their activities are being disrupted by it which can, in my humble opinion, only be a good thing.
These units should not only be accepted but actively supported.
LM