Are you sure that this isn't some cunning wording like ' the amount available to you is £200'?
This is quite a usual stunt that includes the extent of your approved overdraft in it and is designed to enable you to forget that if your balance goes below £1000 (in your case - because you have an approved overdraft of £1000), you will actually be paying them some money for the privilege of running your account.
Welcome to the world of running your own financial affairs, by the way.