Scratching my head

Hello, new member here!
The missus has brought a 55 reg landrover freelander MK1 TD4 HSE mainly to run the pooch around in. Its not without some minor issues as to be expected for its age, so naturally its a bit of a project for me.
Yesterday I was giving it a quick pressure wash to get the thick mud off and noticed the ringlight around the ignition barrel was on. Then noticed the interior cab lights and luggage light was on. When push the switch on the main interior light it's just on both ways on the switch. It only goes off when you hold the switch half way in. But, the rest of the interior lights stay on. When all doors are shut, the "door open" light goes off on the dash display. It's my job to have a look at tomorrow so it'll sit on the drive tonight with its lights on again! I'm a little bit stumped until I get into it so just wondering if anyone has any suggestions of where to start?

The interior lights will be on the whole time the doors are open, they can't be switched off on this model.
You can also put them on when the doors are closed by the switch on the light itself.

Now as the door open warning light on the dash is going off, it means the body computer (called the Central Control Unit or CCU) is getting the door closed signals from the door lock assemblies, which is good.
However as the interior lights are staying on, it means the drive MOSFET in the CCU has likely failed, which is bad, unless you know someone who's good at repairing electronic components.

There's one test you can perform to prove the CCU is at fault. Leave a door open for 20 minutes, as the CCU should detect this and turn the interior lights off to conserve battery power. If however the interior lights stay on all the time, then it's very likely that the switching MOSFET has failed in the CCU, which will need replacing by someone who knows what they are going.
This diagnosis assumes that the wiring hasn't been messed with by a previous owner.

So I have had this failure once before. Thinking back it was caused by a duff contact in the drivers door lock mechanism.
When the door unlocks it signals to out the lights on before the door is actually opened. This contact had failed. Changing the door lock solved the problem.

Testing the ccu as above is a good way to prove ccu is OK. Then I would look at the door lock feed to the ccu next.

Thanks for the very informative responses, clearly some very knowledgeable people on here! I do have a vehicle electronics guy and a mechanic that I'll go to for anything that ends up being quite complex so it looks like that's where I'll end up! I've taken the fuse out for now as a temporary measure for driving at night and to stop battery drain. I'll look at it again in a couple of days when I've got some time and try the door test, see how it goes. I'll cross my fingers that the lights go off as that sounds like it'll end up being a fix that's easier on my wallet but it'll be what it'll be! Thanks for the guidance!

Good luck ! There is not a lot in it cost wise.
Second hand ccu, check you get 3 or 5 door to suit is around £30. Door lock about £40 , don't buy second hand as they will be as worn out as yours !!
Labour about 1 hour each I'd say.
With a new or replacement ccu you will need to just get the remote fobs reprogrammed.
I can do that but am in North Devon and need car and fobs.