I rang the garage and they just reiterated what they originally said. They said there were no codes given.
Their report was:
"This was their diagnostic report
"Diagnostic Report

Have ran full diag on vehicle and no codes relating to fault described bit didnt access the bcm
Managed to gain access to bcm (after a few love taps) and found it wasnt communicating to the immobilizer module reset it and it was working but lost communication again and could gain access to it
Tested lights and found resistance was higher in driver side light signs of corrosion
new bcm and headlight to fix. may need to come into garage to code in"

I'm reluctant to disconnect the alarm if the hazards lights are flashing when i'm driving.
It is ironic - I have had a horrendous few years what with family members dying and relationship breakup and major health issues on top. This car was supposed to be a bit of enjoyment.