They send people lots of scary letters. I got at least 4 or 5 the year before last (when I didn't have a TV or license), getting more threatening, telling me I was the subject of an official investigation, etc, etc. They never actually did anything about it. Since you're not breaking the law you're under no obligation at all to write to them. I certainly wouldn't waste the time and money on a stamp. When they say that "you need to write to us" to tell us that you don't use the TV, they're lying. They can only enforce the law if you're breaking it.
(Don't stress about the "£1000 fine" either - that's the maximum allowed by law, the actual fine given is usually closer to £100, and they can only fine you at all if you've actually broken the law!)
(Don't stress about the "£1000 fine" either - that's the maximum allowed by law, the actual fine given is usually closer to £100, and they can only fine you at all if you've actually broken the law!)