Hi Chris
I use exactly the same methods as George, unfortunately my roof is 9 meters from ridge to gutter so requires two roof Ladders connected together. Wire brush and scraper is the best method for cleaning, a power washer although quicker only serves to create a rough surface for moss and lichen to adhere to in the future. You also need to remove the downpipes to prevent drain blocking.
A lightweight tower scaffold is ideal for gutter cleaning, especially if you're not confident on a ladder.
When I do get my roof cleaned I'm going to research spraying a clear tile sealer which is supposed to help prevent growth and staining but I've heard mixed reports on its effectiveness.
