Be aware of the escape route via the boot.
Don't put the car in park if the invalid key message is displayed until you have got to somewhere you can escape.
2 keys in the car is a bad idea as you need one manual key outside to open the door manually.
If you really are worried push your dealer to apply the update asap. Keep and manual key secreted under the bonnet where you can direct someone while locked inside, to let you out rather than via the boot.
This is the best summary of what we know I think is the thread lilleshall linked below, there maybe a more recent I don't think so though.
Post in thread 'Locked in my MG4 & unable to escape - Serious Safety Issue'
Locked in my MG4 & unable to escape - Serious Safety Issue