Runway material
Its well known in the village that when the runway was constructed they used surplus ash material as a cheap filler from the nearby ICI plant.
The ash is causing it to slowly sink according to ex airport workers. Dont know how far its sinking per year but probably not much. Peel tend to only patch the taxi ways, or only resurface the centre part of taxi ways due to the cost.
Elvington was used as a standby for the space shuttle flights incase they needed to return in an emergency due to its length. Top gear also use it sometimes, but the hamster Hammond tends to wander off line.