I know how you feel, I once 'reported' a new Mum to my Health Visitor as I felt that she was not looking after the baby properly. I won't go into details, but it was not child abuse, more like ignorance. It obviously wasn't just me as the Health Visitor just said that she knew about this woman, and it was all being looked at.
Actually I wish I had the guts to do what you've done about a couple in the village where I live. There's a couple that live on benefits (definitely), he's on disability, and whilst you will never see him working in the front garden, apparently they've got a very nice back garden. The wife works as a cleaner, privately, for a few local people, and this money is not declared. But I would still feel awfully guilty about 'shopping' them. Everyone else in the village knows about them, and if no-one else has reported them, how should I, as an relative newcomer, react to this?