problem with cast guttering

I own a property which has old cast guttering fitted. It is probably orgional and getting for 100 years old.

The problem is this. It is a terraced house and 3 houses share the down pipe. I am in the middle of the three and niether of the neighbours bother to clean their gutters.

When we have a downpour the water cannot get away and overflows from the gutters into my bay. The bay is flat roofed and runs back into the gutter, thus the water just overflows under the felt and swoosh into the bedroom.

Is there a simple fix I am missing ?

I was considering installing my own down pipe and blocking off the neighbours inlet to it, is this reasonable and dooable considering the guttering is pretty damn old and the profile may not be available.

Water should not flow back into the eaves, so you may have a separate problem with rotted roof felt. But it depends on the design of the eaves and soffit

The simple fix to to offer to clean the neighbours downpipe and gutter if he can't be bothered

You can't just block off the gutter from the neighbour upstream of you - he has a right to use neighbouring guttering and downpipes

I have cleared the neighbours gutters and I am fed up of doing it.
I should have pointed out that the gutters do not go around the bay they go straight through the bay and the bay runs backwards toasted the gutters.

I do not intend to block off the neighbours entry into my gutter ( although I am tempted).
But what I may do if filter his inlet with some mesh and keep his crap build up on his side.

The mesh option sound a good one to me, it may prompt them to start clearing their own gutters when theirs start overflowing on their own property rather than yours.

I'd raise the clip on each side of your guttering slightly so their water stays in their gutters, maybe when their gutters are overflowing they might become more considerate.

Every house should have its own drainage system.