the metal bars that come out to lock on my double glazing door wont?

If you open the door and try 'locking' the door whilst open you will know if it does 'lock' then there is not a fault with the actual lock mechanism and adjustment is only required either on the hinges or if the door has 'dropped' then the glass needs re-packing (Toe & heeling).
If it still doesnt lock in the open position then you probably need to buy a new lock mechanism.

Mike at Agree-a-price frames
September 2010