It would be good to have a large scale tidal project somewhere as a pilot project so even this one isn't financially viable it would be a step in the right direction.
The French have had one on the river Rance for years but never built another one. I don't know if there are any data publicly available.
It was our first stop,
when we left the Portsmouth - St. Malo ferry
when we visited a couple of years ago.
If you believe the French government figures for an
ego-boosting national project:
http://en.wikipedia.org/wiki/Rance_Tidal_Power_StationI remember reading in the visitor centre,
it took many years for the ecology of the
'dammed' zone to recover to anything like what it was
before construction,
and,
some species have not returned.