that deep, huh?
The FAA have got a computer program which calculates the required thickness, taking into consideration a load of variables including max aircraft weight, number of T/O and landings, typical weather experienced etc.
For today's "heavies" the total depth will typically be nearer 36 inches, depending on the thickness and material used for the top surface - concrete v asphalt.
Sadly, I cannot find the thickness for Stansted. At Schipol, there is a layer of 7 inches of prestressed concrete over a foundation of some 32 inches of various aggregates.
Sad but true!