This downpipe was blocked solid due to the joint collars having an opening that was too small. Cast iron joints like this are now only manufactured with this smaller 45mm diameter at the sleeve which is too small & tend to get blocked easily at the off set bend. This is a prime example of the problems joint collars like this cause. We always use good condition reclaimed cast iron which has the correct aperture to allow unimpeded rain water flow.
This is a length of iron pipe that was lodged inside the downpipes.