Welcome to this customer to customer forum.
Please can you please provide BT Wholesale speed test results for different times of the day, including the further diagnostics page?
These must be done using a computer connected to the home hub, using an Ethernet cable.
This is needed before a moderator can be asked to look at it.
If you could run the final test when the speed is slow, as its the last test that has its results stored on the server.
Can you also provide the name of the exchange you are connected to.
I cannot help you, as I am just a customer.
You need to post the results of those tests here on this thread.
Once that is done, and the drop in peak time speed can be seen, then a moderator can be alerted, to look at the results, and take some action to resolve it with BT Wholesale.