Wayne, I was with Blueyonder until they became Virgin and then I moved to BT. If Virgin hadn"t taken over I would still be with the cable supplier as I think it"s the best broadband you can get.
Any company that relies on phone lines based on BT technology, which is pretty much all except cable, have a theoretical max band width which cannot be exceeded without a major overhaul. I know of no one who has come close to the theoretical maximum, due to line quality, distance to the exchange etc. You also need to use filters attached to your phone line otherwise phone, internet etc suffer.
With cable, I"m not sure what the max band width is, but it"s got to be at least 10 times that of BT technology.
You never know what you might need your broadband for in the future, Wayne, and is £14.95 really that expensive ? If I were in your shoes (and it was still Blueyonder), I"d be sticking with cable.
You could also phone your cable company and tell them you"re thinking of moving because you can get a better deal elsewhere. They just might reduce the price or offer you something in compensation.......
Just my humble opinion.