Sarenco, I feel you're pain. Similar situation to you except while I'm within the 100/200 metres that insurance companies ask about I'm also well above the water level of the river, even in a flood situation which they don't ask about.
The river has flooded in the past (3 times) but extensive flood relief work has been done. What really frustrates me is that even with 3 flood events my home has never been flooded in its over 100 year of existence. But PeteB is right, if the flood mapping software says no then no it is.
My only glimmer over the last few years is that my current insurance company (through the AA) continues to cover me, with a heavy flood excess in the last few years - had some row over that, only agreeing with it in the end because my argument that the house is unlikely to flood negates worrying about any excess. I do try shopping around but never with any success. I'm dreading the day that the AA refuse to renew - they'll have some fight on their hands at that point.