We evaluate the action of Hecke operators on Siegel Eisenstein series of
arbitrary degree, level and character. For square-free level, we simultaneously
diagonalise the space with respect to all the Hecke operators, computing the
eigenvalues explicitly, and obtain a multiplicity-one result. For arbitrary
level, we simultaneously diagonalise the space with respect to the Hecke
operators attached to primes not dividing the level, again computing the
eigenvalues explicitly.Comment: to appear, Internat. J. Number Theor