Almost as much as the additional benefit provided by the third runway. Heathrow currently estimated to generate £6.8bn of GVA annually which would equate to >£400bn over 60 years.
Oh sorry, I thought this was the Manchester thread. I seem to recall one or two members from here got the red card when they ventured onto the LHR and R3 threads.
It's strange how a few like to denigrate or belittle developments at Manchester Airport.