Can I ask neighbours to put in their own downpipe?

[LarryForPrimeMinister]

1950s houses, semi detached. Next door are housing association if that makes a difference.

Their guttering at the back is connected to ours and we share a downpipe down my side.
The problem we have is that when it pours heavily my guttering can't take all the water from two houses and overflows.
They also have a giant tree at least 50 ft in their garden that they said they would remove but haven't so that clogs it up too but even when not clogged guttering is struggling.
Can we ask them to put in their own downpipe to take pressure off ours? It happens every year and it's getting annoying.
Edit: no other houses on our street share downpipes so not sure why ours is the only one.

I can understand that

When you say they have a drain their side what do you mean? A surface water sewer? Or a manhole cover? Or a gully in the garden? Because a downpipe would need connecting to something which normally means digging up and laying pipes.

You will have more chance with the HA than the neighbours I’d suspect but even then they may well say no, that’s just how the houses were built. My house has the manhole cover in the garden and next doors foul sewer runs into my manhole so all their shit comes through (underneath) my garden and if there’s a blockage it’s me that has to rod it all. I wouldn’t just be able to tell them to get their own sewer.

If they can't get a new downpipe fitted you have a couple of options to improve things

• You could get the gutters separated at the boundary line, but have the initial bit of downpipe separate before joining into yours (or even fit a parallel downpipe all the way down to the gulley in the floor). Then if their guttering isn't cleaned it doesn't spread into yours, and any overflow is on their property.
• If it really is the volume of water rather than leaves blocking the gutter then you could also fit a larger downpipe. but I very much doubt the downpipe is the issue.

Does it overflow from the top of the downpipe, or at the bottom, or from some of the joints?

Photos may help. Also show the gulley or ground at the bottom of the downpipe please.