I did it and it was brutal. The misleading bit of the course description is “14km unsurfaced” or something like it. Basically means great big craggy rocks and slippy slate interspersed with the odd bog.
Trained by running up and down the North Downs and the usual long rides so was fairly well prepared.
When it came down to it I just wasn’t up to the mark. I was languishing with the back markers as one by one they dropped out, I kept going and got a (forty!) second wind as I saw the Ribblehead Viaduct. Hammered the road setion but missed the cut off at the bottom of Pen y Ghent by 1 min 30. Pretty gutted but gave it a go.
Great scenery, great race, great people, but as suggested above, lots of fell running would be by far the best training.