Identified at last :)

[Grimley_Feindish]

Finally tracked down what teh algae is that is growing so well in my tank -
Staghorn Algae

http://www.aquaticscape.com/articles/algae.htm#staghorn

I guess some more thorough searching to start would have turned up some
results but better late than never.
It's not entirely unattractive (I'm with Netmax on his views of algae) but
it's hard to remove form plant leaves.

--
Alan