JDK I think the arrival would have crumpled more than the planing hull as Windermere is up to 500' deep in places which would allow sufficient speed to build up to bend quite a bit of metal. Did Sunderlands have fabric covered ailerons as well? Surely the covering wouldn't have survived 60 years in the water.
Having the facilities of an offshore exploration department available to me I whizzed a copy of the pic over to our sub-sea survey department. The comments were:
a) The starboard wing should have a 'shadow' at the trailing edge not both leading and trailing edges.
b) The texture of the picture on the aircraft would be different to that of the seabed regardless of how long it has been down there. There isn't the level of marine growth in Windermere necessary to blend a structure into the seabed.
c) The line going from top to bottom to the right of the aeroplane would need to be about 12" in diameter to cast the sonar shadow shown. Its straightness would suggest a pipeline and, as far as we know, there are no pipelines like this running along the bottom of Lake Windermere.
So, again, tis a fake sir!
PS On zooming in, I can see that the tail turret is in fact missing.