Abstract: Our interest here is in the laminar-turbulent transition of a plane channel flow driven by a pressure gradient (plane Poiseuille flow). To this end we consider large Reynolds number structures consisting of the strongly nonlinear three-dimensional interaction between a roll/streak flow and a so called lower branch Tollmien-Schlichting wave. These travelling wave equilibrium states have recently been demonstrated to be the large Reynolds number continuation of computationally generated structures from the full Navier-Stokes equations, where they have been demonstrated to act as ‘edge states’, separating trajectories which will return to the laminar state from trajectories which will eventually become turbulent. The transition process is often observed to involve the formation of turbulent spots, and in fact the numerical solution of the nonlinear interaction equations tracking these states into finite amplitudes, shows that these states localise in the spanwise direction.