Shared supply question on billing & installing own supply

KJUKManc

Hey everyone, not sure if this is the right place unfortunately as I couldn't find a sub topic but it does tie in somewhat with what I want to ask.

I've been having issues with the stopcock in my kitchen, it needs replacing and I've contacted United Utilities over the location of the outside cut off or main street valve.

They've said they have no records for our street (~1910s build ) and to get a plumber to freeze & squeeze. This is likely to be impossible due to location and we really need it isolated to swap.

Since then found out (kinda realised) we're on a shared supply. I was going to ask for a meter to be installed bypassing the issue above but they can't.

I thought we were as I could always hear people running taps (mid terrace). The issue with the stopcock is horrendous humming and vibrations when neighbours run their taps, and now us! 

It's been getting worse and I've exhausted all my skills and it's really time to bite the bullet.

Through reading up about a shared supply I've realised it maybe more cost effective to just have a new mains installed. I have a cavity under my house which is around 5ft below street level and it's literally 3m to the front boundary. It would just be a case of having a trench cut for the PEX. 

No need to dig internally and I can access under the house if needs be to have the connection done like that. Atm it would mean ripping up flooring but we don't need to worry about laying a trench through concrete for example.

Worth mentioning I have no idea whether it's lead going to the current stopcock as it's copper to the floor in the kitchen. Underneath for all I know it could be copper and there may even be a mains cut-off somewhere, when I laid the hall flooring there was an MDF square lid right where the door mat would be inside. It can't be gas as that's coming through to it's own box and the electric is under the stairs, so I'm thinking there could be a valve there and then the shared line from that point.

My biggest worry is that the water line actually goes along the whole back under each house & from house to house along the back internal cavity wall and that MDF is just an access point that was used for some installation or repairs over the years on other things.

Whatever is the case, I still want our own mains connection. We have really bad pressure, I'm about to get quotes for a new bathroom (currently only walk in shower) and obviously want it all done properly. Plus I'm sick of hearing when neighbours use the toilet/taps and obviously need this stopcock issue sorting asap. 

Now my questions are -

*Who do I get to do this? I know the waterboard will do from the boundary line.

*If I don't have a mains cut off in the hall and it's actually as I'm worrying (one pipe down the entire back to each house) how do we go about this. How do we even at the very least isolate to sort the stopcock or even if we ended up with a leak? If for now I just get the issue with the stopcock going crazy, how can they work on this? It's behind a kitchen unit but the back panel could easily be cut but there's no way to isolate with no mains valve location. Also worth noting I've looked high and low on the street. Spoke to neighbours who've just shrugged their shoulders. Deeds have no mention of location neither.

*As it's a shared shouldn't our rates be divisible by the number of shares on the one connection? We pay full rates. If there's only one mains and then it splits, aren't we being charged wrong. We've been in this house 18 years and always paid full. I wouldn't actually question this until we're on our own line.

*Shouldn't the water supplier make every effort to locate the outside point? How can they have no records of the actual street location? If there was a leak outside they're responsible on the highway, yet they're telling me zero records for my entire street. It's a main road! I had to press them to check a side street, they came back telling me there was a fire hydrant point but no records of anything else. This is also where I believe the main line comes from as it's one straight line down the back from that point. 

*How can a plumber do any work when they can't even isolate or interrupt a shared line? My understanding is they need permission?

I know this is a lot but I'm pulling my hair out.

Thanks