UK Ford Repair Questions? Ask a Mechanic for Answers ASAP
If you remove the air intake pipe and look inside where the crankcase breather is plumbed in you may find evidence of oil.
If you do find oil replace the valve. If this is all OK then its possible that the valve stem seals are past their best and are drip-feeding oil into the intake. These can be replaced without removing the head by a competent garage in half a day or so