  We present results for QCD with 2 degenerate flavours of quark using a
non-perturbatively improved action on a lattice volume of $16^3\times32$ where
the bare gauge coupling and bare dynamical quark mass have been chosen to
maintain a fixed physical lattice spacing and volume (1.71 fm). By comparing
measurements from these matched ensembles, including quenched ones, we find
evidence of dynamical quark effects on the short distance static potential, the
scalar glueball mass and the topological susceptibility. There is little
evidence of effects on the light hadron spectrum over the range of quark masses
studied ($m_{\pi}/m_{\rho}\geq 0.60$).
