Unlock the central locking -
Unlock the central locking - now on the tailgate tailgate push the plastic flap ( the one you normally pull BACK to open tailgate ) FULLY forward towards front of car, now lock and unlock central locking the lock mechanism can now align properly. Now lift the tailgate look under the black trim piece above licence plate, where the licence plate illumination bulbs live, and at each end of the plastic flap you will see the hinges are rusty, spray some lubrication on the hinges and work the handle until it is free to spring FULLY forward when released. This problem is caused by the rust on the flap hinges stopping the plastic flap going fully forward when released, it may only me 1mm off its stop, but its disconnects the lock mechanism. Spraying some lube in there every 6 months will stop it happening again.