This is the Thames corridor, if anywhere can become the new silicon valley (with all the wealth and education present in that area) it is the LHR site.
In fact, you could say that LHR is a complete waste of space that is holding back the west of London from becoming the the most advanced area in Britain. Don't we have a duty to release that potential, and allow the Thames coridor to spread its wings and achieve its full potential?
I'm not sure that you can describe what is still the world's busiest international airport, and which as Skippy says is able to maintain consistently higher yields than other comparable airports, as waste of space?
You seem fixated on this idea that LHR would release vast tracts of land for re-development. For better or worse, LHR is about as compact as it is possible for such a large airport to be. Where else will you find so many large aircraft jammed in between two runways, with a few others overspilling into T4 / cargo / mainternance areas?
Unlike surface transport infrastructure, those runways enable connections to most of the globe - all within what - 6 sq miles approx?
I challenge you to come up with another airport which generates the kind of yield / economic opportunity per square mile that LHR does - as there aren't many if any that do it outright. Maybe LCY would be up there! Ans as for this Silicon Valley - they need connections too, and LHR does that.