Locked In
Except for the fact that they try to lock you in (each time your contact is expired) for another 2 year period (TalkTalk do) so you can obtain the lowest possible price (halves the monthly cost in many cases)...
However, if you change your mind (say 6 months down the line) they charge you an early termination penalty (in the case of TalkTalk that is 16 Pounds per month remaining on the contract)!! This is in many cases enough discouragement to just stay put.
So not exactly a competitive environment in which the customer can "take back control"...