(if cable is not smothered in insulation) - we have vaulted ceilings so cables runs between roof and 100mm celotex and in the walls between terminal bricks and plasterboards without conduits. Roof can get hot in the summer, but there is a air gap between roof and celotex to prevent condensation.not to worry. as i said, both oven and hob will be fine on a 32A MCB, 6.0mm cable (if cable is not smothered in insulation) . this application of diversity has been in use for 60+ years and found to be compliant. only reason to install separate circuits for oven and hob would be to isolate either if faulty and still have use of the other.