I love Ronald Turnbull's work and I found an interesting picture on his website
http://www.ronaldturnbull.co.uk/pics/geopix/Pages/16.html It reminded me that I'd seen a tombolo at Low Ling Crag on Crummock Water. Waves diffract around objects that are roughly the same size as the object if the object is round. The island looks far too big for it to be this. I have posted before about knife-edge diffraction round the ends of a long narrow island
http://wigtonphysics.blogspot.co.uk/2014/06/knife-edge-effect-diffraction-and.html I would suggest that it is this that has happened here. The diffracted waves will have brought sediment from both sides and deposited it.
