What does it say for handback speeds in the chart on the BT line check both impacted and non impacted.

Handback speed
Clean 55 Mbps
Impacted 49 Mbps

That's the problem Openreach may say speed is acceptable. You can call your ISP and say you have heard noise on the line but if it is not there when Openreach visit you run the risk of a no fault found and a charge from Openreach. Who is your ISP?

EE

Btw is tbb speed supposed to be so low?

It's from the thinkbroadband speedtest

Those speedtests you have linked to aren't too bad perfectly adequate for most needs including HD video streaming and general downloading. The average uk download speed is 59 mb/s. You will be hard pushed for EE to do anything unless it is below the handback speed on the BT page. The impacted figure.

I was refering to the 6 Mbps tbbx1 download speed I got this morning

Well that is very low but what was the TBBx6 speed? You should also try a few speed testers around the same time like speedtest.net and fast.com to confirm to identify what kind of speed problem there is.

Usually in speedtests my tbbx1 speed is around the same as the http speed

but since this started, my tbbx1 speed has been a lot lower

This morning my tbbx6 speed was 7.6 Mbps

Afternoon speed was 8.4 Mbps

Evening speed was 14.3 Mbps

Right now speed is 11.4 Mbps

I see what you are getting at the TBBx1 speed I just looked at the total speed at the top of the speedtest links. That smacks of congestion somewhere but you should also check it with another speedtester as mentioned above. Speedtest.net and fast.com have single thread testing options. Once you have proved it is not the speedtester providing erroneous results you can go to EE and complain about streaming quality, the gaming latency may also suggest congestion somewhere. What is your machine spec and are there any other users on the LAN?