Hi M8
Cat D means that the insurer decided not to repair for whatever reason(uneconomical,owner did not want it back,they could bridge the gap with the salvage value...etc etc)this is the category for the lightest damaged vehicle and means that it is repairable but they just did not bother....
there is usually no bother re-insuring these,occasionally the insurance company will ask for an engineers report,but not always.....so if its cheap and it looks repaired ok its probably a decent buy.........
Rob........