Your bank should write to you.
With a few rare exceptions, you won't be charged just for having an overdraft limit, only when you borrow using it.
The changes mean a switch from sometimes-complicated systems of fixed fees, to interest charged in direct proportion to how much you borrow and for how long.
In general people overdrawn much less than £1000 benefit from this, whereas those overdrawn by much more are hurt by it. Though it varies by the bank and your account terms.
For example with Barclays, under the current system being overdrawn by £50 for 7 days would cost £5.25; being overdrawn by £999 for the same 7 days would also cost £5.25! Under the new system that £50 over 7 days would cost 28 pence, while the £999 would be £5.75.
Far from "the majority being penalised for the feckless", it's actually those trapped in very large overdrafts who are hardest hit. And those are the people who are potentially least able to move the debt somewhere else.