One of the problems with LHR expansion (and LGW) is that the airline business makes promises on flight numbers to get their way and a few years later tries to expand the numbers way past the original scheme - thus no-one believes a word we say and even small improvements meet die-in-the-ditch opposition every time
You're mixing up cause and effect. People who know what needs to be done understand that the only way most of our fellows might buy it is to lie, then allow a few years to pass. No one believes a word of it because no one wants to face the reality of a painful price required to ensure we have growth to pay our very substantial debts. The idea there is some fantastic way around this is a childlike naivety. Democracy is all "me, me, me" and very little "us".