I've just received a survey about expanding Heathrow, accompanied by a pamphlet about how vital Heathrow is to London. Needless to say this comes from Back Heathrow, the organisation that wants to expand Heathrow, so not exactly unbiased. Neither is the survey, the wording is all in their camp even though they do ask about alternatives, and the survey document contains another page of pro-Heathrow "information"
I suppose that I should be grateful that they are at least being honest about where they're coming from, though I suspect that the results will be spun to make it appear that this is an independent result.
In other words, this is a text-book example of a biased survey, and more or less worthless as real research. I'm not planning to return it.