Could be a fault on the MDF in the exchange, as that is where the phone and broadband join together. Perhaps an unsoldered connection?
There are quite a number of connections at that point, and many older exchanges still have soldered connection blocks, and not IDC connections.
You need to request a quality check by an Openreach Frames Technician.
Upload speed will always be most affected by bad connections.
It needs an exchange visit. An SFI (Special Fault Investigation), if they still exist.
As this has been going on for a while now, I will ask a moderator to help.
Hi @SherlockPhones,
Thank you for posting, I'm sorry if you're experiencing a fault with your service. If you send me your details, I'll be able to run a few checks on your line and send an engineer if needed.
I have sent you a private message with instructions on how to contact the team. You can access your messages via the envelope icon at the top right of the screen, or click on this link, Private messages
Thanks,
Paddy