Flooding subfloor 1930s semi

[sealed]

Hi,

Floorboards up for some structural building work and found almost half a foot of rainwater underneath house.

It doesn't smell so I suspected it might be a leaking rainwater pipe. Our neighbour has a gully that collects the rainwater from both our roofs. The downpipe is on his side. I put some dye in there and it showed up inside our house.

Water company have been out digging up my patio to find the pipe marked on a map that should run across all properties but after digging 1m hole haven't found a pipe!

Is it possible, the water company's map is wrong?

And is it possible that the neighbour's gully may just lead to nowhere other than a broken clay pipe that is leaking into the clay-soil and then into our sub-floor?

Has anyone fixed a similar issue?
My feeling is that we have two options:
1) Get the neighbour onside (dig up his patio!), and reinstate a new pipe from the gully into an effective soakaway.
2) Cap the gully and direct their water into a soakaway/rainwater butt on our side?

They've been quite difficult so far - opposing planning, insisting on Party Wall Award etc.

Thanks

 

[JP_]

When I had my extension done the builders reported a collapsed rainwater drain which was just leaking into the ground (luckily away from the house)
I would guess the cleanest and safest option is to have new drainage channels dug to a soakaway, but if the downpipe is on your neighbours side you'd need to access it.

Could the pipe on the records be connected to drainage - maybe it goes under your house and is leaking there, rather than being somewhere in the garden

 

[sealed]

When I had my extension done the builders reported a collapsed rainwater drain which was just leaking into the ground (luckily away from the house)
I would guess the cleanest and safest option is to have new drainage channels dug to a soakaway, but if the downpipe is on your neighbours side you'd need to access it.

Could the pipe on the records be connected to drainage - maybe it goes under your house and is leaking there, rather than being somewhere in the garden

I think I've ruled out it being connected to drainage. Helpful neighbour on other side ran hose into their gully and I looked into manhole for foul sewer (also under patio) but no sign of the water from rainwater gully at all.

Downpipe is directly next to our house so access is easy. Presumably, local water company will not be responsible as soon as they've ruled out the existence of a shared surface water pipe?

We also found a clay 'soakaway' pipe leading from our subfloor into the garden - presumably for groundwater as house is on a hill. It was blocked with silt but there are also cracks in the patio so I think it's proably cracked too.
Do you think it would be best to dig up the whole patio, dig a new drainage channel for the rainwater for our property and neighbour's, cap neighbour's broken gully, and a put in a new pipe for our house's groundwater channel. All could lead to a soakaway with a silt trap?

One problem though is that our soil is London clay. What are the alternatives to a soakaway for clay soil?