Having now had time to look at many hundred images on Google, I am very confident of the ID of an intermediate phase Gyr. The big doubt is about its origin.

At 11.15 this morning I was approaching black rock from the Cheddar Gorge road when I noticed a large bird perched on the rock. My first thought was a very pale Buzzard as it had a creamy head and pale grey/fawn coloured plumage with white edges. It flew and I immediately realized that it was a Falcon. It then circled a bit further up the valley, showing slightly spread primaries, and was mobbed by a Crow (definitely not a Jackdaw as it was calling) which showed me that it was at least Buzzard size and wingspan. It seemed to me to have slightly bronze colour under the tail but pale grey/fawn elsewhere. There was no head pattern or dark under wings. Having researched the possibilities I can only make it a Gyrfalcon-probably an escape but great to see.