The One plan was £17/month according to the BBC article, I know they have a £15/month option for unlimited data, so what is the fuss over?
Some of the outrage is over the sudden notification, on relatively short notice, that they'll be doubling your bill unless you act otherwise.
They could have given a longer notice period, moved you to a plan that suits your actual usage instead of the most expensive one, etc.
The timing is poor too. 3's 4G network is not very good, even if you have 800MHz 4G in your area, you need one of a handful of phones to have any chance of using it (and the priorities are set such that you won't go onto it if you can get any 3G signal at all). They should beef up the network and then announce a price rise. But doing it this way is just going to drive more people away