Improved Wilson QCD simulations with light quark masses

We present results from simulations using 2 flavours of O(a)-improved Wilson quarks whose masses are about 1/3 of the physical strange quark mass. We present new data on the mass of the singlet pseudoscalar meson and evidence of the onset of chiral logarithms in the pion decay constant. The previously observed suppression of the topological susceptibility at lighter quark masses is confirmed. We report on the performance of the hybrid Monte Carlo algorithm at light quark masses.