Does anyone know anything about it? Does it have reasonably dense wood?
(it's supposedly hardwood, although at that rate of growth i find it
difficult to accept). Also i dont want to plant an invasive
fast-spreading species that will upset the neighbours!

It's Paulownia tomentosa, It's a pretty bad weed in parts of the US, not
so bad in others.
http://nbii-nin.ciesin.columbia.edu/...do?specieId=83

It's extremely brittle wooded (I can snag a branch on a sleeve and break
it off without damaging my shirt, and the
one I've been trying to kill here (and all its nasty little offspring)
produces a wood that burns far faster on the bonfire than douglas fir or
vine maple. Looks like it's getting weedy in Germany also:
http://www.lboro.ac.uk/research/cens...tracts_r-t.htm

And it looks like it's escaped in Britain in at least several instances:
Hill, M., Baker, R., et al., (2005). Audit of non-native species in England.
English Nature Research Reports N° 662, English Nature.

Kay