Measurements of CP violation in B 0 → J/ψ K 0 S , B 0 s → J/ψ φ and B 0 s → D − s D + s decays play key roles in testing the quark-flavour sector of the Standard Model. The theoretical interpretation of these observables is, however, limited by uncertainties from doubly Cabibbo-suppressed penguin topologies. With continuously increasing experimental precision, it is mandatory to get a handle on these contributions, which cannot be calculated reliably in QCD. In this summary, we discuss a data driven method based on the SU(3) flavour symmetry of QCD to relate the penguin contributions in B 0 → J/ψ K 0 S , B 0 s → J/ψ φ and B 0 s → D − s D + s to unsuppressed counterparts in decay modes with similar dynamics. The fit results obtained with the currently available data are presented for all three modes. In addition, we discuss prospects for the LHCb upgrade and Belle II era, and illustrate the possibilities for the determination of hadronic parameters.