A data processing system is provided with a programmable memory protection unit 10 defining a plurality of programmable memory regions 2, 4, 6, 8 each with associated programmable memory attributes. A default memory protection unit 22 is provided and defines a plurality of default memory regions a, b, c, d, e each with associated default memory attributes. If a miss occurs in the programmable memory protection unit 10, and the memory access is a privileged level memory access, then the default memory protection unit 22 will return default memory attributes for that memory request.