On Wed, 11 Jan 2012 11:29:45 +0100, Martin wrote:

You'll still have to mechanically remove what is already there but
a
regular wash down with a copper salt solution should stop it
returning. I'll leave it to the reader to find out which copper
salt
is the most effective. B-)

You'll find that that is also illegal.

Meh, who is to know?

And a nice decorative strip of copper along the top edge of the drive
is a decorative strip...

--
Cheers
Dave.