The evolution of current and temperature profiles in JET has been analysed using an advanced equilibrium analysis code and absolutely calibrated ECE measurements. It is found that during the discharge 'flat-top' the evolution of the current is well described by neoclassical resistivity. However, during the discharge rise phase, the current penetration can be more rapid. The MHD processes influencing the rapid penetration are discussed qualitatively by analysing the trajectories of several discharges in the (q0, qa) plane.