From what I've been able to find there are no specific rules or laws on spreading ashes. Generally though its seems spreading on public property is not allowed but is frequently done. Pretty much a don't ask dont tell kind of thing. I can see where some people would be offended is they knew they were standing or playing amongst remains. I would however not have a problem with ash remains being scattered into the lake as almost all of it is a sand like bone and will sink right to the bottom. This should certainly be done out in the middle of the Broads in my opinion but I'm sure there are some here that would find this practice unacceptable and I'm not suggesting it should be done. If you do scatter in the lake then I would certainly stay far away from FLL's intake pipe though.
I've wanted to be scattered on top of Cannon Mt and I really see no issue with that.