The answer if anyone needs this in future is that the base seat cushions have a black handle on the lower edge which release it from a set of runners. Now I just need to find out how to remove the back of the back seats!

Also, the rear seat cushions weigh a combined total of 16kgs - they aren't even leather!

__________________
UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!