Thanks for all the helpful comments guys
appreciate the input
First job on the list is to remove the seats and carpets and dry the interior out, leave it for a week to dry out and then see if any electrical faults have disappeared. I've already drained the boot out so that no longer has any water in it
Will check all the earths in the footwells, I suspect the ones on the passenger side probably have quite a bit of corrosion.
On a positive note, yesterday I started up the car to move it a little, and the highline satnav screen turned on! The screen just stayed blue but it turned on so it's a start
Will try and get some photos up over the weekend if I get time to remove the carpets and hopefully get some photos of the underside.