It begins with a throwaway comment over breakfast, innocent and knowing, the way that teenagers can be. My 16-year-old son tells me he has been supplied with alcohol by a man he doesn't know. He's been buying it regularly for a year, and he's not the only one. The man's number is passed around the school playground. You can text him your order ? vodka, whisky, whatever you like ? and he will meet you in an alleyway to exchange goods for money. He charges the same prices as the shops, so the kids can afford it.

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