When I moved into this house, there was a lot of extraneous wiring. Phone line extensions that went nowhere, that kinda thing, so I ripped out everything back to the master socket by the front door.
When fibre was enabled, I had a visit from an Openreach engineer, reporting a fault detected on the line - the case was the old master socket had some corrosion, so he replaced it with a new one.
However, I want to move all my network gear to the under-stairs cupboard, and branch everything from there. As I don't use a landline, this would mostly just mean Wi-fi and a few ethernet cables.
There's a not insignificant cost to have Openreach come out and move the master socket, so I'd rather avoid that. It's also not something you can really do yourself - the master socket marks the point in the connection where the providers responsibility for the wiring ends and yours begins. If you tried to move it yourself and screwed up, there's a significant charge to that too.
Just using a phone extension lead works, but slows the broadband speed noticably.
Unfortunately, due to the age of the phone system and it's various evolutions over the years, finding decent, up to date information is not as easy as it should be.
I manged to put together a DIY solution that boosted my broadband speed by approx 50% (~14 Mb download speed with regular phone extension, to ~21 Mb using my solution)
This was done by combining a few other ideas and sources of information.
This is what worked for me. Your results may vary, and usual "don't try this at home" warnings apply.
Moving the master socket without moving it
I found this guide which shows a master socket with 'A' and 'B' connections, which it states, you can run to another socket using CAT5 network cable, which will have a similar effect to moving the master socket, as it bypasses a lot of the filtering of the sockets, and CAT5, being twisted-pair cable, has better shielding qualities than regular phone extension.
But unfortunately, my master socket is the newer type 'NTE5C' socket, so it doesn't have the same connections.. It does have a similar A and B connector, but it's on the provider side of the socket, and is in use, so I don't want to mess around with that.
It give me an idea though. Even if that route is out of the question, a lot of the interference comes from the cabling used. If I were to create a phone extension lead from CAT5, it should still be an improvement to a regular phone line.
Pins 2 and 5, according to the first article, are the equivalents of A & B.
So, what if I put in a telephone extension using that connector like in the video, but instead used better cable as per the article? In theory, the speed should improve due to the increase in cable quality, but would lose a bit because a microfilter would be required (because it's not been pre-filtered.)
I also thought, if CAT5 beats regular phone cable because it's twisted pair gives it some shielding, then wouldn't something more shielded so even better? I had a usable length of co-axial cable, the type used by satellite dishes and antennas.
This is a single copper core with a mesh-like shield all the way around it. These would provide the connections to pins 2 & 5 (I used the core for pin 2, the shield for 5, but I don't think it'd matter which way round).
The article does recommend solid core wire, which the core of the coaxial is, but the shielding is not, so I guess there may be some performance trade off there.
This was wired to a regular phone socket under the stairs, in which there's a microfilter and the router.
Initially the speed fluctuated a bit, but once it bedded in, it settled on a speed (as reported by the router) of approximately 21Mb, which is up from the approximately 14Mb that was achieved with the same length of regular phone extension cable.
I'd be tempted to experiment further (ideally with something with twin solid cores and shielded.), as there's still a bit of room for improvement - at the master socket directly, the router could get 26Mb - but for now it's fast enough.