Got a call last night from my wife telling me that the Nav screen was on showing the splash screen. It then went off and came back on a short time later.
All this whilst the car was sat on the drive locked and not driven for a day or so.

Anyone know why this does this?

I could be way off with this, but... I believe the system wakes up and checks the air suspension every so often. I know this because I had a leak in a hose and it kept trying to level, until the reservoir was empty, even when switched off. I was thinking you have something waking up? Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

I've never seen that before. I'll keep an eye on that. Cheers

Splash screen is showing every time the system wakes up something is definitely waking it up could be the suspension but also other systems that are connected to the I-bus ( radio,nav,light module,...) if it happens often it wil drain you're battery quickly as it uses several amps to wake the modules.

External radio interference?

The old favorite water ingress in the LHS of the boot... Check for damp and do a battery reset

Just been woken by the cars alarm. Bleeps for a few seconds, stops then does it again.
I went out to the car and the little amber LED near the gear selector is on, along with one on the drivers door window switches. All doors are locked.

I'm hoping this isn't a repeat of last year when I had to have a new battery

bonnet alarm sensor Noddy...they get corroded or stuck ......