Roger Tonkin wrote:

Our house faces north, and as such the tarmac drive
gets no sun at all and is quite damp.

I've tried over the years removing the moss that grows
by scraping it off with a spade and blasting it off
with a power hose. Neither of which work really
successfully and are starting to damage the tarmac.

So it looks as if it must be a chemical attack, but
what with? I,m hoping to get to a garden centre next
week, so I'd like some idea of what has worked and
what to avoid if possible.

Many thanks

Have a go with coca-cola - seriously.

Full strength coke is a good, cheap and easily obtainable cleaning
agent. Personally, I've used it for removing oil stains from concrete
which it does very effectively.

.... which is why I can not understand anybody putting the stuff inside
themselves ...

Larry