Thanks again for your help.
The alarm was installed by a very experienced electrician, who we've used previously for other jobs. He hasn't been able to solve the issue.
Seems like the alarm isn't working how it should and that the below comment by Amps is the solution;
A system installed to EN50131 should create a tamper alarm but I always program for a fault alert which turns the navigation pad red and the keypad beeps.
As its not obvious to us how to implement this change, and on hearing comments that the ion16 isn't a great panel, I'm coming to the conclusion that a replacement is required.
Can anyone recommend a well priced/wireless replacement alarm system that I can research? Thanks.