If you are within an agreed overdraft limit, then no there isn't a charge.
If you are above your agreed limit or are overdrawn without a limit, then yes you will get charged.
From NatWest's website:
Interest: Over agreed limit 16.5% (EAR 17.81%). Typical 17.81% EAR variable.
If you exceed your arranged overdraft facility or go overdrawn, you will be charged �38 for each unpaid item (Standing Order, Direct Debit or Cheque). You may also pay �30 for any default notice we may need to send to tell you that you've breached our agreement.