Interesting as this only happened recently and I had been getting speeds in excess of 350Mbps when testing on Speedtest.net.
I checked my NIC and set it from auto to 1.0Gbps Full Duplex under Speed & Duplex (don't have a Link Speed). My NIC is a Realtek Gaming Gigabyte Lan Interface. My cable is a Cat6 Professional Gold Headed Shielded Cable. Checked my speeds on my phone & tablet and getting the same speeds as the PC, so I can rule out the Cable.
Just updated my NIC drivers and nothing seems to have changed.
Have you checked the 'Check Service Status' at the top of the page ?
If nothing is showing try phoning 0800 561 0061, this will tell you of more local issues that may be affecting your district. Be aware that it isn't a manned line.
Go round all the accessible internal and external co-ax connections and ensure that they are finger tight.
If everything above is OK we need do some more troubleshooting; to start with …
Disable any VPNs that you have running.
Can you set up a Broadband Quality Monitor (BQM) at thinkbroadband.com - this will give you an insight into what is happening with the signal at the other side of the Hub, it will take a few hours to get any kind of trend showing although you should post the link straight away.
Post a 'Live Link' to your BQM on here.
Instructions for posting BQM Link
Under your BQM graph are two links in red.
Click the lower link (Share Live Graph) then click generate.
Copy the text in the Direct Link box, beware, there may be more text than you can see.
On here click the Link icon (2 links chain to the left of the camera icon)
In the URL box paste the link you copied and in the ‘text to display’ box write My BQM then click OK - you can post the link straight away.