Just a quick update. I called UU on Saturday and explained the situation, they were remarkably reasonable about it, even said it wasn't a problem. I'm now paid up to date and have a DD set up. There were no penalty fees or anything. Thanks for the calming comments, and advice!

Thanks for the reply, that makes me feel a lot better! I'll get it sorted tomorrow, and thanks for all the extra advice, its good stuff to know.

18 months ago I moved out of my parents house into my first flat (renting) I thought that I'd set up all of my payments (gas, electric, council tax etc), Today I received a letter from united utilities saying they have recently found that my address is occupied and are going to send me a water bill. I've looked over my previous statements, and yes, I didn't inform UU that I'd moved in. I know this was extremely stupid! Obviously I have to ring them and sort this out, I have the money to pay for 18 months worth of bills, but am just afraid of what to expect when I call. Will they threaten me with legal action over failing to disclose my address? Will it affect my credit rating? if I ring them tomorrow to get this sorted, apologise and offer to pay in full, what kind of backlash/penalties can I expect?