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You have to do speed tests with a wired connection because there are to many variables that can affect wireless connections
If you have a white Openreach modem and a Homehub make a direct connection from your PC to the modem which will eliminate the homehub. Follow this guide to do that. Use your computer as normal and run your speed test. If it improves you will know it is possibly a faulty hub. You obviously will not be able to use any other devices while doing this.
Step 1: Remove the homehub from the modem
Step2: Connect your pc/laptop into the modem using LAN1 port
Step3: Open network and sharing centre on windows and click set up a new connection or network
Step4: Connect to the internet then click make a new connection Broadband PPPoE
Step5: Username firstname.lastname@example.org and the password as BT
Step6: connect, If it doesn't,keep pressing try again until it does.