In this paper we give a general method, based on the ordinary representation theory of the symmetric groups, for computing the irreducible components of their permutation modules over a field F of coprime character istic. We apply this method to determine the decomposition into irreducible submodules of the F[S_n]-permutation module on the right cosets of the normaliser in S_n of the subgroup generated by a permutation of type (3, 3).
