jeyes fluid. Mix up a strong solution and apply with watering can,leave for as long as possible then scrape of with spade and wash down as normal. I cleared a very long path this way -it stinks but very effective.
As recommended by an ABer a few weeks ago I used cheapie soap powder, sprinkled over dampened concrete, left a while, then hosed and scrubbed,as pressure cleaner not available.
Yes Jeyes Fluid, I did our block paved drive a few years ago. The air all around the house smelt rather nice I thought, even a visitor in the street asked what I'd used. It got rid of the moss and cleaned the brickwork.