The existence of travelling wave type solutions is studied for a scalar reaction diffusion equation in R^2 with a nonlinearity which depends periodically on the spatial variable. We treat the coefficient of the linear term as a parameter near certain resonances and we formulate the problem as an infinite spatial dynamical system. Using a centre manifold reduction we obtain a finite dimensional dynamical system on the centre manifold with fully degenerate linear part. By phase space analysis and Conley index methods we find conditions on the parameter and nonlinearity for the existence of travelling wave type solutions with particular wave speeds. The analysis provides an approach to the homogenisation problem as the period of the periodic dependence in the nonlinearity tends to zero. Joint work with Adam Boden.