LHR is renowned to have a few ghosts. I read a chapter in a book once a long time ago and have a few faint memories - perhaps someone can enlighten:
There was a plane full of horses that crashed near 27R on the site of T1 shortly after the airport opened - can't remember exact details but apparently there are some ghosts associated with that.
There is also a ghost in one of the central car parks and a chap in a pin-striped suit and bowler hat has been seen on 27R.
More recently however I read a story about a motorist who was driving East down a deserted M4 late one night near the LHR junction and saw a figure of a woman in white standing in the middle lane. The motorist woke up her boyfriend who was asleep and didn't see anything and then turned off got, back onto the Motorway and went the other way. This time they both saw the figure. They turned around again at LHR and headed back towards London by which time the figure had vanished. This event occured in 1994.