Problem Solved!! The Secret Fuse...!
I actually found the solution to this ages ago and neglected to post it here (I posted it elsewhere).
Anyway, you need to change 'the Secret Fuse'...! This is a cunningly-hidden fuse since it is for the OBC and factory alarm system.
Here's how you find it:-
Remove the BACK SEAT by lifting it from the front sharply so it pops out.
The rear seat base is held in by two big metal spring clips, each of which enter into two retaining slots - the secret fuse can be seen by looking into the slot on the left-hand side of the vehicle. So if your cars is LHD, look into the slot behind the driver seat, otherwise, it's the passenger seat.
You will need some long-nose pliers to get it out. It's a 15A fuse if memory serves me correctly.
I'm quite confident you will find this fuse to have blown, and a quick change will have everything working again.
Let me know how you get on?
All the best!