I can understand why the CAA might have wanted all 737 Max flights to stop - but surely if they have the power to forbid flights, they must (eventually) have the power to lift the prohibition, and also (in the interim) to have the power to grant exceptions...
I assume TUI made some sort of behind-the-scenes appeal to the CAA to fly it to somewhere for long term storage that is less remote and away from the sea with 2 very senior pilots flying under very specific conditions. Why would the CAA not relent in this specific instance ?