Lets bring some economics and capitalism to this debate. We have been told for a century now that Lhr is full. Yet it keeps on being able to find slots and room for more pax and new services. I believe that although runway capacity may be near 100% at Lhr, only about 70-80% of seats are sold on services. I could be wrong with my percentages but I am certain that aircraft do not operate through Lhr at anywhere near 100% load factor. We are also told that there is a waiting list of 30+ airlines waiting to get into Lhr, some waiting for years. I would like to see that list myself to see how true that is! Because if I was running an airline into London, one of the greatest markets on earth, I think I would give Lgw a try rather than do nothing for years in the hope of getting a slot at Lhr. At the end of the day, if the only expansion is at Lgw and the demand keeps increasing, the airlines will go there as there will be no-where else to go. And no, they will not up sticks and go the Paris etc, because the carrot which is London is just too big for them to resist.
There is a lot of posturing going on here and self interest. For many, including Easyjet, they do not want Lgw expanded out of self-interest, not the good of the nation. People may have to deal with their obsession with Lhr and learn to think outside the box. Markets change, so do travel patterns and airlines.