In this work, a new mathematical model to describe axial and lateral mixing in fluidised beds is presented. The model is an extension of previous versions of the countercurrent backmixing model (CCBM) that were restricted to axial mixing only. The fluidised bed is divided into parallel 'mixing columns', which are convective currents induced by the bubbles. Each mixing column has a central upflowing stream of solids and two adjacent moving downwards. The practical application of the model requires a minimum knowledge of the bubble properties and the definition of one empirical parameter: the exchange coefficient between countercurrent phases, K, The model can be rapidly solved with the proposed algorithm and reproduces semi-quantitatively the main features observed in mixing experiments carried out in a bidimensional fluidised bed of coal and PVC as tracer.