Worth pointing out that there are two locks on the gearshifter. One is the mechical lock activated by the key turn as amply described above. The second is an electrical lock that prevents the gearshifter being moved from park unless the foot brake is being pressed.
If you encounter a stuck gearshifter first check you have working brake lights. If you do then it is likely that the mechanical lock is at fault as described above but if you don't then there is an electrical fault. There are two likely causes of an electrical fault - either the brake light switch has failed or you have had water ingress in the central electrical module (CEM). First check the brake light switch -pull it and check for correct operation/continuity. If this is not the problem then you need to inspect the CEM. Instructions on how to inspect and remove can be found on YouTube eg
https://m.youtube.com/watch?v=U8UozG9qLvM&t=229s
In the case of my car there was very clear evidence of water ingress. I removed the CEM and sent it to Prolux Electronics (advertises on eBay) and had it back the day after they received it. Once reinstalled the gearshift worked perfectly again. On reassembly I took some steps to waterproof the wiring loom tray below the windscreen as I suspect it doesn't drain as it should any more and instead caused water to track into the CEM.
It is possible to move the car with this fault but there will be no brake lights so don't use it on the road! To move manipulate the manual shifter lock so that the shifter can be moved to neutral with the ignition off. Then start the engine, depress brake and move to Drive or Reverse. Once you put it back into Park it will be stuck there and you will need to switch off and repeat the process to move again.
Finally a couple of other things worth pointing out:
1) the fault could also be the electrical lock itself but this appears to be unusual by comparison to the other causes.
2) CEMs appear to hold vehicle specific information so it is not straightforward to swap to another one. Repair is thus the less inconvenient option and is inexpensive.
Good luck!
Nick