"veritas 8 alarm that was fitted in 2001"
I think the above is the reason it activated with the power cut.
Has the panel ever been serviced or had a new battery in the 8/9yrs it has been fitted, I doubt it.
The problem is your battery in the control panel, it should have been replaced at a max. of 5yrs.
Best to find an engineer I think.
acorn
January 2010