you planted a Norway maple *on purpose*? why on earth would
you replace a weed tree with another weed tree? why not with a
red maple, a sugar maple, a beech or some tree with actual
value?

Uh, the original poster, if I'm guessing right from the address, was
in *Europe*. At least in parts thereof, the Norway maple is native.
See map at http://linnaeus.nrm.se/flora/di/acera/acer/acerplav.jpg (I
don't know if the UK is considered a problem or not for growing this
tree).

Agreed that I would not recommend planting a Norway maple in the
United States (at least not in the mid-atlantic region where it has
escaped cultivation and now lives in wild areas:
http://www.nps.gov/plants/alien/pubs...antic/acpl.htm although I'm
not sure that advice applies to all areas).

fortunately my state has wised up and banned the sale & intentional
propagation of Norway maples.

Please, say which state. Location does matter in these things.