A week or two back, I wondered if my comments to a BBC comments thread had been censored, as my reply sat in a moderation queue for four days, while the argument raged on without my contribution. Eventually my comment was released, with its link to a file of correspondence relating to the CRU's withholding of climate data deleted. According to the email from the moderators, this was because I had linked to a PDF file, something that is apparently against site rules.
I thought at the time that this was odd, since another commenter had posted a PDF link shortly after mine. This other PDF was posted by someone on the warming side of the argument.
Now one of the other commenters on the thread has got in touch to say that he had pointed out to the moderators the doctoring of a quote by another commenter, saying that this ought not to be tolerated. For anyone who followed the thread, this doctoring was done by the same commenter whose principal line of argument seemed to be to accuse everyone else of lying. And also the same one who managed to post a PDF unmolested by the moderators.
The moderators felt that doctoring quotes was OK.
So, according to BBC moderators, it appears that accusing other commenters of lying is acceptable. Doctoring quotes is acceptable. And posting PDFs is acceptable so long as you adhere to socially acceptable norms on the subject of global warming.
It's probably something to do with the unique way they are funded.