I can't remember, I think the Media Standards Trust did some research on that.
One thing I just wanted to add, if I could, is the issue of proportionality. In the BBC's editorial guidelines, before it has its own small list of what represents the public interest, there is a two-line phrase which for me would need to be incorporated into any statute or definition, which goes:
"When using the public interest to justify an intrusion, consideration should be given to proportionality: the greater the intrusion, the greater the public interest required to justify it."
That seems to me to be a perfectly good, succinct way of approaching this whole question, which is proportionality.