Hi Chris, I would suggest getting a code scan as well mate as it could be something locking out the security starting process, and it may make tracking it down faster for you maybe worth the fee for a mobile mechanic who can do that for you as I doubt it will be a fuse or relay causing it sounds,like something in the security side of the process.
I am sure if any others have ideas they will post it, these are just guesses on my part so I hope you get it sorted fast mate
KAA