How to clear blocked cast iron downpipe - can I drill an access hole in the bottom and stick a drain rod up?

[michael123123]

With a garden growing up there, I am not surprised it's overwhelmed. Therefore a closer diagnosis is necessary. Maybe there is no blockage at all. The sky garden could be restricting flow.

Both sides slope towards the down pipe, and I've cleared my side as best I can. The vegetation on the other side I would only expect to back up into my neighbours guttering. The down pipe runs between our two houses, just ever so slightly on my side of the boundary.

 

[DiyNutJob]

Both sides slope towards the down pipe, and I've cleared my side as best I can. The vegetation on the other side I would only expect to back up into my neighbours guttering. The down pipe runs between our two houses, just ever so slightly on my side of the boundary.

Your photo shows something growing your side. Tomato plant perhaps? Rather than speculating, get a camera up there and see. The area is easily accessible via the window.

 

[freddiemercurystwin]

It could be the photo, but there definitely looks like something is growing out of your side. Even a mirror on a stick would do.

 

[datarebal]

You are going to need to get up top or get another to do it . The gutters blocked for a start . You will not clear the swan neck from ground level . It looks like it has been renewed in uPVC anyway at top.
The soakaway might be blocked but you would usually see water leaking out of the d p joints