Joseph and Hodges-Levasseur (in the A case) described the spectra of all quantum function algebras R q [G] on simple algebraic groups in terms of the centres of certain localisations of quotients of R q [G] by torus invariant prime ideals, or equivalently in terms of orbits of finite groups. These centres were only known up to finite extensions. The author determines the centres explicitly under the general conditions that the deformation parameter is not a root of unity and without any restriction on the characteristic of the ground field. From it he deduces a more explicit description of all prime ideals of R q [G] than the previously known ones and an explicit parametrisation of SpecR q [G] .