Two interesting newly-published books on Heathrow:
Heathrow Airport - Operations Manual (Haynes) is a glossy, accessible insight into the day-to-day workings of the airport. Given the extensive access clearly granted to the author, it's not surprising that parts read like they were written by Heathrow's
PR department, but it's fascinating nevertheless.
Heathrow - From Tents to Terminal 5 (Amberley) is written by a civil engineer and concentrates on the buildings and infrastructure. Illustrated with (mostly) B&W photos and line drawings, it's essential reading for those who know their beam soffites from their secant piles.
Both available from Amazon.