One of the truly Great things about Britain is that if you're 15 years old, shoving heroin in your arm seven times daily, living in a graveyard, well, someone has to help. You probably don't want the bloody help: the outreach worker, the benefit clerk, the children's home – they can all quite literally "do one". As Robyn in Dispatches: Street Kids (Mon, 8pm, C4) proves, by the time you're a pile of bones, covered in scabs, carrying everything you own in a small Superdrug carrier bag, you're not in the mood for another grown-up and their "good ideas". You don't want to be in their system. But this is what we do.

The system doesn't run like clockwork, but there's a wonky plan in place nevertheless. OK, there was a plan as I typed this column. Funding for Robyn and the other 100,000 children made homeless each year is currently being financially pruned in the spirit of "fairness". God knows who's supposed to give a damn about Robyn, then.

Maybe only television production companies? Maybe George Osborne will watch Dispatches this week and realise how compelling children Sophie, Haydon and Chelsey are when sobbing about their "pain" and their "journey". Sky1 could start a privately funded, benevolent TV experience called Britain's Next Top Junkie. Don't just sit there snivelling, kids! Prove to Tess Daly you really want a bed for the night. Let's cut that ruddy welfare umbilical cord!

For anyone currently ruminating on ideas of social "fairness", this Dispatches is beautifully illuminating. Homeless teen Sophie, 17, found herself blatantly on the back foot in Britain's pecking order three seconds after the requisite parts of her mother and father clashed and made a zygote. Sophie was taken into care aged two after her mother – who appears in the documentary clearly enjoying the sound of her own voice – went out for a night taking acid and speed, leaving her baby with a child. It's not the anecdote that's crucial here, but the way her mother recounts it 15 years later. Still with zero levels of self-awareness or remorse. Still quite sure this whole palaver is Sophie's grandparents partial fault for not giving her weekends off to go raving.

Nowadays, Sophie coasts from sofa to sofa living with much older men who like having sex and taking drugs with her. At one point, out of desperation, Sophie attempts to live with her mother. "You weren't making any progress," the woman says, clearly recovering from having her irony glands freshly removed, "So I thought it was time for Mummy to step in." Isn't this going to be a tough time? Surely there's a lot of hard feelings here? "Oh no, I just seem to have a very maternal instinct! And now she's here I see it as day one of a new life and I've got my daughter back!" Sophie stays for two days and then runs away.

If I worked as a social worker, Osborne wouldn't need to make me redundant, I'd be fired for "unacceptable client shaking", following a meeting with Sophie's mother. Life, Dispatches writes in block capitals on your forehead, is horribly unfair. We can chunter about "blame" and "roots of problems" and how the soft-soaping must end but we've also got a long British history of accepting that kids like Robyn and Sophie need a leg-up in life too. "I used to sleep in bed at night with a massive blade under my pillow when I was a little girl!" Robyn tells us, "And the funny thing was, all sorts of stuff went on in that bed and I never used the knife. I don't know why!" Robyn giggles to indicate the punchline of her tale.

She's going to need to workshop this routine more before she takes it on Michael McIntyre's Roadshow. No one's laughing. "I've just got this dirt inside my head," she says, "And I've tried jagging it away and shagging it away and snorting it away but I can't make it go." I look at the self-harm marks up her tiny body, then think about George Osborne cutting local council fundings and I can't decide which are the unkindest cuts of all …

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