I've found more problems with the telephone line into the particular house than I have with most dial-up ISPs. In my experience, the "free" (usually 0845) ones are as good as the paid-for dearer ones. When I was still using dial-up, I never had problems from our hideaway in the mountains, but had regular disconnects from the "main" place.
Now, both are on broadband, and ... guess what?
If you can afford £15 a month, broadband has a lot going for it!