I don't wish to be accused of Jesuitical nit-picking (any more than I would speculate as to what, if anything, goes though the mind of the average Maule driver), but the 1978 Byelaws for the control of power driven vessels on Lake Ullswater apply to aircraft other than flying boats only to the extent that they are "designed to manoeuvre on water".
As for Paragraph 137 of the ANO, I am far from convinced that any activity with a 100% safety record could be portrayed beyond reasonable doubt as being difficult, let alone dangerous.
Fly safely,
Jacko.