It is 7.30 in the morning. The doorbell goes. Half dressed, I stumble downstairs. “Who the fuck are you?” says this guy, as I open the door, wiping the sleep from my eyes. I mutter something about being the vicar. “Sorry for the bad language, Father,” he replies, as he walks up to punch D in the face. Later, I piece together what has happened. D, a well-known local user in desperate need of heroin, has spat at a group of people sitting outside Tesco. D says he is going to slice one of them open and their mother too. He menacingly draws his finger across his own face and makes several disgusting racial insults. A local security guard and another passerby decide they have heard about enough and set about D. Outnumbered, D runs to the vicarage for sanctuary and rings my bell, just at the point where his pursuers corner him on my porch. Later the police arrive, everyone is questioned, and a bleeding D is led away in handcuffs.

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D has form. Earlier in the week he had rung my bell, this time in the middle of the night, asking for money. He knows I won’t give him any, but he’s desperate with uncontrollable shivers, piercing migraines and terrible cramps in his legs. He can hardly stand. Can he get methadone from A&E, I ask? Apparently not. He tells me the only way he can get methadone is if he gets arrested. The police have access to it, he tells me. As the police arrest D after that morning’s fracas, I wonder if he has got himself arrested deliberately.

The home secretary, Theresa May, was just down the road in Brixton this week. “Police custody is a place where a number of dynamics meet,” she said. “It is a place where dangerous and difficult criminals are rightly locked up. But it is also a place where, all too often, vulnerable people, often with mental health problems, are taken because there is no other place to go.”

The presenting issue for May was the number of people who have died in police custody – 17 between 2014 and 2015. And she was obviously right to insist that this, and official obfuscation in seeking redress, are totally unacceptable. But what she didn’t follow up with is why so many people with mental health issues are finding themselves being dealt with by the criminal justice system in the first place.

Of course she didn’t, because what she won’t admit is that the police are being used as a mop-up social service, as a way of addressing social issues that fall through the widening cracks of the other social services being eviscerated by austerity. For example, during the course of the last parliament, the budgets of mental health trusts were cut by 8%. Budgets for drug education and treatment were also slashed. These things have consequences. And they are experienced, first of all, on the streets, and by the police.

D is a classic case in point. The police have to sort stuff out that other people don’t know what to do with, or haven’t got the resources to deal with. Like vicars, they are often the last stop in a game of pass the parcel. And they do it with 17,000 fewer frontline police than they had in 2010.

Which is why the constant hassle the police get from Theresa May feels a bit rich. The Tories cut the budgets of our social services and then blame the police when they are unable to cope with the consequences. But crime is down, says May. Yes, it’s been dropping since the 1990s as, among other things, cheaper, more effective security technology has significantly altered the criminal calculation of risk and reward.

But violent crime is on the rise again – up over 20% in England and Wales in the last year. And it feels noticeably up around a vicarage located between the two boroughs – Lambeth and Southwark – with the worst records of gun and knife crime in London. All of which inevitably brings yet more people to the vicarage door. If you want to understand the full social consequences of a shrinking state, you don’t need to take it from lefties like me. Ask the police.

@giles_fraser