Having cut out all the panels I matched them all up and clamped the same ones together at both ends, put each bundle in turn in the woodworkers vice on the bench and carefully sanded down to the lines with a belt sander. The advantage of using a sander and not a planer was the sander had a more gentle action in removing the waste wood and the panel edges didn't require hand sanding afterwards, so it did two jobs in one. Bloody noisy though! Hence the ear defenders.
Next job is cutting out the butt joints.