I am going to follow up on Jim's suggestion and use some kitchen worktop veneered with screw fixed ply, probably 9mm. Cabbie has very kindly offered to try and get me a suitable off cut piece of worktop.
I'm considering putting some self adhesive cork floor tiles on the ply to provide an easily pinnable surface. If and when they wear out I can pull them off the ply without worrying about damaging the surface and then flip the ply over as Jim suggested.
At the moment, due to space restrictions in the ruins out back, roughly describable as a garage, I'm going for a size of 1800 x 600mm