'Reverse ferret' is a term used in the British newspaper industry to denote a sudden and complete about-face on an issue. There are numerous examples, but by far the best-known is the sudden shift in media coverage of Diana, Princess of Wales. Before her death, she had been hounded by the tabloid press, prompting her to make a PCC complaint in July 1996. She was also vilified because of her relationship with Dodi Fayed. (Unfortunately, I can't find the original articles among all the sentimental (and just plain mental) crap on the Internet. Do please /msg me if you know where to find them)
Princess Diana's death forced a major change in position, particularly since Prince Charles publicly blamed the paparazzi who were pursuing her for the accident. As such, Britain's tabloids began a campaign of very loud public grief, fuelling sickening nationwide mawkishness that didn't abate for months. British satirical magazine Private Eye captured the hypocrisy perfectly with its cover, which had the headline 'MEDIA TO BLAME' above crowds of mourners remarking on the difficulty of finding papers with grim details.

The term is thought to have been coined by Kelvin Mackenzie while he was editor of The Sun. He referred to the hounding of individuals, invasion of privacy etc. as 'putting a ferret up their trousers'. When the coverage overstepped the mark or started to obviously violate the law, he'd rush into the newsroom yelling "Reverse ferret!".

(Etymology added 21/05/2008, thanks C-Dawg )

See also:

Obsolete: 10 years of turning in the grave (with the Private Eye cover):


BBC News report on the accident: