How much anti-social behaviour in the UK is due to undiagnosed mental illness ?

For the past decade, i've occasionally pondered the rise of anti-social behaviour in the UK. Why have so many of my fellow British become so casually aggressive, violent and anti-social in so many ways? My wife made a point last week that has stayed with me. As a north American , she's much more in tune with the 'therapy culture' , something the British have never been comfortable with. Her point was that perhaps Britain is seeing a near epidemic of undiagnosed mental illness ( to varying degrees of course). Look at the amount of Brits who 'self-medicate' with drugs and drink, and suddenly this point gains plausibility. The now infamous video of a middle aged woman throwing a cat in a trash can for no apparent reason ( See BBC news UK ) really drove the point home to me . The woman was later identified, and a 'mob' cornered her at her house. But she didn't need a mob and retribution. In North America the first point that would have occurred to people is : ' My God - the poor woman is clearly ill . She needs help, she needs a shrink !' Perhaps that cultural difference in the reaction is itself a clue to why the UK sees so much more of this behaviour than somewhere like Canada.
A less extreme example ( since perhaps the cat woman was obviously nuts ) was the woman who urinated on a war memorial, performed a sex act there, then fled court. My reaction was ' regular saturday night in UK' , my Canadian wife's, quite seriously : ' What the hell is wrong with that woman , is she nuts ?'. At first, I laughed, then I thought : ' Maybe you've got a point. Maybe she is kinda nuts. And that's the real issue here.'