I'm sorry for the problems you're suffering with your speeds during peak times.
I've run some tests and I can confirm you're affected by F004311662. This is the reference for ongoing investigation work in the area, our engineers are currently planning some broadband upgrades to support an increased demand for our services in your area. Once this work is completed, you'll find that your speeds (especially during peak times) return to normal. The current review date for the work is 5th October 2016.
I'll send you a PM with a bit more info about this issue, including details of how you can claim a credit for the loss of service. We'll keep you posted of further developments as and when we know more.