Barely anything about it on the BBC or Channel 4. It's not very prominent on most newspaper websites, and the ytend to suggest that if there was a threat, it's from a couple of years ago. I think someone may have been pulling the Daily Mail's leg (or they just made it up):
Claims that the security services foiled a plot by terrorists to fly an aircraft into Canary Wharf, London's tallest building, were played down last night by senior Whitehall officials.
Anti-terrorist sources said they were unaware of any plot to attack the tower, though for some time they have had it on their list as an obvious "iconic target".
"The assertion is surprising", said one well-placed official, referring to claims on ITV and in the Daily Mail newspaper.
The reports also named Heathrow airport as a target. Unlike Canary Wharf, the airport was mentioned in computers seized by Pakistani authorities in early August.
http://www.guardian.co.uk/terrorism/story/0,12780,1357526,00.html