They are Eucalyptus trees which grow extremely fast, these two were only five years old and already about 30/40ft high. They need loads of space and constant lopping to keep them from getting too tall.
So these two were planted far too close to the wall at the end of the garden, the left one was actually leaning on the wall and the right one wasn't far from it. The garden behind is about 12ft below ours so you can imagine the height of the wall when you're standing in their garden.
The trees sway an awful lot with high winds, it'll be a nightmare if one day they break the wall and what if someone was in the garden at the time... Uh-Oh.