Sounds like congestion.
Use this speed tester then scroll down the page and carry out the further diagnostics. This test must be done with a wired connection.
If you do this once when the speeds are as they should be and then once when the speeds have dropped. Do not run any more diagnostic speed test after that.
This will notify BT who, if they don't already know, will upgrade the capacity. It may take a week or so for that to happen.
It won't fix its self if it's congestion but all you can do is wait. BT Wholesale should be aware of it and will be in the process of fixing it.
I will do that, it seems like every person I’ve told this issue to just says wait and the BT people too, I just fed it’s a copout and they’re saying if you wait it will hopefully fix itself
You can't just wave a magic wand and extra capacity will appear, it requires more infrastructure to be installed.