Recently, Daimler hyped up the smart fortwo's high-mpg ability by claiming in a television ad that you can go from London to Edinburgh, a distance of over 400 miles, on one tank of petrol fuel. This caused some - well, five - complaints that the ad was full of it. The UK's Advertising Standards Authority (ASA, whose website features a big "How to complain" button) investigated and decided that the ad's claim that, "on one tiny 33 litre tank, a smart car can do 433 miles," was not misleading. Mercedes said that the smart fortwo 71 bhp petrol coup used in the ad was capable of "73 mpg [Imperial] at an average speed of around 40 mph." So, you might be able to make the drive, but not very fast.
While on the ASA site, I found these other recent decisions: "There is probably no God" bus ads are OK and cookies are not a health food.