Apologies for shouting, but handy hint of the week, being made public due to the shear incompetence of the way the short stay parking is organised
Park in the Short Stay Car Park at the North Terminal. Doesn't matter which one, 5 or 6. Keep your entry ticket safe.
When ready to leave, drive to
LEVEL 3, CAR PARK 6, it is signed as Car Rentals.
Drive through the barrier, no ticket required.
If challenged apologies profusely and drive around the level to the exit.
At the exit to Level 3 is another barrier. Press the button to receive an exit ticket.
Proceed to the main Car Park Exit.
At the Exit barrier, insert your second, freshly acquired ticket, and enjoy your journey home
The reason for keeping your original ticket is that you may well have to pay. This is a considered risk, and in no way unreasonable.
Obviously this is ultimately the responsibility of the driver who uses this little ruse, and it should be duly noted that actively avoiding paying for parking is probably very naughty.