White van gone green and black (2 replies)

What was a white van has been sat under trees for 12 months and is now covered in really stubborn black/green algae.
Even a very powerful jet wash with vehicle shampoo won't shift it.
There must be hundreds of white van men on here and loads of caravan dwellers.
How do you clean yours ?
Bring back the Ideal Home Exhibition I say !!
What's the magic product ?