I'm afraid I'm going to go against the concensus here. You have a contract with the bank, the terms and conditions of your account. If those T&C's say that if you go overdrawn, we will charge you £X, then that is all they need to tell you.
If you want to continue using their money, rather than your own, knowing full well the consequences, then that is up to you.
As the banks always say, if you dont like it, close your account and go elswhere.
For once I tend to agree with you, however a friend of mine opened an account many years ago, which would not allow you to go overdrawn at all, he would go to the cash machine and if he had no money in his account he could not draw it out.
So the bank move the goalposts and remove this block without telling him and he goes overdrawn. I this right.
Also I have just opened bank accounts for my son's (14 and 16) and they cannot go overdrawn until they are 18. Why the heck can't the banks just keep block on an account if you ask for it.
Tha banks do it on purpose to make more money out of people.