Posted: 01/06/2014 at 09:36
Something I know!!
It sounds like Cuckoo spit, it's just a little green bug that excretes the bubbly substance, as far as I know it's nothing much to worry about, I've got it all over a hedge, and so long as you don't sit under it, it's no problem at all, the rain usually washes it off.
Have a quick google for more info