TonyR,
My mistake, I should have written low wing configurations are more unstable rather than low wing aircraft. As aircraft designers, one would assume, have sought to combat that!
According to my notes:
For low wing aircraft, the principle being that the airflow over the fuselage generates an upflow of air over the lee wing (outside wing) increasing the lift of that wing and hence increasing the angle of bank (which is the definition of unstable) rather than decreasing it (the definition of stable).
However, dihedral directly combats this effect by reducing the angle of attack of the lee wing. Swept wings provide a stabilising influence too, to do with amount of wing directly presented to the airflow.
Apologies for my rather anal contribution to this thread but I like these discussions because they add a dimension of realism to my studies.