Hi Picklock, is the exterior of the blocks rendered, and is there any damp patches on the inside of the walls? Check all your gutters and downspouts are clear and not leaking and also the drains they empty in to., and you should be good to go. If the walls are dry on the inside, your spec sounds fine to me. If there is visible damp on the inside, and it is not coming from faulty gutters etc, then use pressure treated timber lath, celotex insulation, then tack building polythene (visqueen( onto the laths, and fit the boards. The floor is unlikely to be insulated under the slab, but will (or at least should have) a dpm under it, and if the floor is totally dry, sounds like there is. Dampness is more often a product of poor ventilation and leaking gutters and roofs than anything else.