Welcome to the club, Ian.
I have the same car as you and used to have the same fault.
The way to release it is fairly simple, but a nuisance.
You must disconnect the battery, making sure you have the radio code handy and the ignition key in your pocket.
Reconnect the battery after a couple of minutes, and the alarm will go off. Switch off alarm and then start the car and following the instructions on the message centre [[Apply footbrake and handbrake simultaneously]
You will have to put in the radio code and reset your settings -- sounds, windows etc.
Just one thing -- it happens to me when it is cold and the battery is a bit low. If the battery is fully charged it never happens.
Regards,
Peter.