Phileas Fogg that second picture of Davidstow looks the part. I do not recall anything prominent in the vicinity, just that we found the runway only when we were on it.
I'm still fighting my memory that it was near Perranporth, but other stuff I have researched from our trip has also proven my memory to be patchy.
Thanks everyone for weighing in. It seems the weight of evidence is indeed on Davidstow. And... I have just found a further corroboration we went that far up. I remember very clearly we saw a road sign for the wonderfully named town of Crapstone, which makes me suspect our route was A395, A30, A388, B3362, A386.