Big thanks to Jungle and this forum for the answer to this problem, solved in 5 mins once I knew the cause.

From his PM:
It was many years ago now, but I do recall not being able to get the car into test mode after a verso tune.

I'm not sure if it’s the same fix for you, but my car actually has two test mode (Green) connectors. There is one under the steering column and another one under a plastic panel next to the passengers left foot. After the verso tune they unconnected this 2nd connector and you need both connected to get the car into test mode.