In article , Christian
McArdle writes
Could anyone advise me on the safe angle a ladder should be at for
working on the outside of the house?

Whatever you do, don't climb up such a long ladder without someone
stabilising at the bottom, or one of those stabilising contraptions. Falling
off ladders is one of the most common forms of accidental death.

It is better to tie off the top of the ladder to an eyebolt fixed to the
house. The person at the bottom can really only stop the ladder bottom
sliding away from the wall. If you start to fall sideways they can't do
much (been there).

Regarding where to get them from, I got mine from Wickes. They are only
"DIY" standard and are priced as such but are fine for occasional use.
--
Tim Mitchell