They might, they might not. ISPs raises prices sometimes, it's a fact of life. You either stay, or you leave. You still seem to be under the misconception that BT Retail's pricing somehow forces Sky and Talktalk to alter theirs. It doesn't.
and as I also mentioned previously, I didn't say it was, but what i was told by 2 reputable ISP's and an openreach engineer.
Saying switch providers is great but eventually they all follow suit (if they follow suit that is) but BT wouldn't be as stupid enough to put the prices higher than the competition without knowing the competitions price would also increase in line with that or everyone would just leave and go else where like you said.
If BT are silly enough to do that then bye bye BT broadband.
I'm with Virgin Media as per my sig, and realistically at there mercy as alternative connection is ADSL2+ at 2mbps