If you would be able to tell us which exchange you are connected to, that would be good, as you may have LLU service from TalkTalk or Sky. In this case, that means that the fact your exchange is 20CN doesn't matter, as LLU service providers provide their own equipment.
If they aren't present however, it may be work looking at Zen Internet. I am with them at the moment, and their performance and customer service are impeccable. I have had some long wait times on their customer service, however this was immediately after a lot of thunderstorms, so they were getting a lot of calls.