The message
from The Natural Philosopher contains these words:

Most of the power would be needed in England (Scotland exports power) so
going too far North would increase transmission costs but don't forget
they get tides on the East and South Coasts as well. :-)

Yeah..why not put a dam across the channel between dover and calais?

Sod the shipping..who needs it?

Hey, we could make locks and charge the whole or Europe congestion charges!

Do not mock.

The English Channel is one of the most crowded sea lanes in the world,
if not the most crowded, but at lower traffic densities a barrage just
might have been a valid alternative to the Chunnel. The Suez and Panama
canals function quite well for levels of shipping traffic well in excess
of that for any single port.

--
Roger Chapman