Dead Van Woes

[Headmonkey]

Hello.
I have a 2013 high top Transit 100 with a dual battery setup.
After not being used for a couple of weeks I’ve found that the central locking has stopped working (both with the fob and by using the key),and that the van is completely dead.
Radio, headlights and the dash info screen are still active, and the immobiliser light still flashes as normal but no dash lights come on when I turn the key and the engine won’t turn over.
I’ve tested the batteries with a multimeter and they are both at 12.7 volts.
This has never happened before. The van has been stood around for a few months as it’s been converted into a camper. However this is the 3rd year of owning it and this is the 1st time that the van has let me down. It was only 2 weeks ago that we took it camping in Wales with absolutely no drama whatsoever.
Any ideas what this could be.
Thanks in advance.

[Headmonkey]

Oops. Sorry I accidentally posted here. I’ve reposted in the relevant section.

[Luke]

no problem welcome anyway