I can only speak from my experiences:
IF a UK police (single engined) helo stoofed into a town centre because its one and only engine stopped / ran down / caught fire, etc etc, it would set the industry back decades to say the least.
Now that we have proven that 90% of the police forces in the UK can afford to run twins effectively, there will / can never be an argument to fly singles over built up areas.
We have a duty of care to the public - twins are available, we have proven that they are viable, end of story.
I have had an engine surge on me, and on another occasion, one of the compressor blades decided to depart the scene. Both resulted in me having to shut an engine down very quickly. Both situations involved me being over the city centre (once by day and the other by night). Was I glad I had 2 engines!!
How in the name of faith the yanks think they could not afford twins - confuses me? If the politicians demanded air support they'd get them 2 or even 3 engined!!!!