Oh dear racedo. LHR pre 2008 was a disaster. Old terminals, cluttered layout, essentially bits falling down. Why would BAA let it go that far? Well they saw STN as the shining great white hope and sunk billions into making it work.
They built it on the back of LHR charges and profits, in effect BA paid for Ryanair's new base. It took a long time to turn that strategy around! LHR got the EuroPier in the 90s an that was pretty much it.