  Early B-physics experiments have left us with a number of puzzles in heavy
flavour physics. New lattice calculations (with a greater understanding of QCD
effects in the Standard Model) will be needed to support the increase in
experimental precision to be achieved by upcoming experiments such as Belle II.
We extend the CSSM/UKQCD/QCDSF studies of SU(3) flavour breaking effects by
presenting new results for the decay constants $f_B$ and $f_{B_s}$.
