Almost too embarrassed to talk about my transmission

Well it's true because what is happening defies logic and I'm feeling like a total novice on this one but this is what happens. My Defender 90 is a 2014 2.2 tdci XS Station Wagon purchased in February with 12500 miles on the clock - currently 14000 miles and was bought as an Approved Vehicle from a Land Rover dealership - it has two years warranty.

In the past couple of weeks I've been getting an intermittent illumination of the diff lock light on the speedometer - sometimes when I'm driving normally on the road and at other times when I come to start the vehicle - it's totally random. I appreciate that this on its own could be a faulty plunger switch in the transfer box, possible faulty adjustment or a wiring fault. But today when it came on I drove a couple of hundred yards up my lane (in a straight line) to join the main road which is sharp right angled turn - on doing this it was obvious that the diffs were locked because I could feel strain in the vehicle and the front wheels were "misbehaving" during the turn.

I was unable to stop the vehicle to do a reverse and then forward manoeuvre because of traffic to kick the difflock, off but as per normal after a mile or so the light went out and I could tell that the transmission had freed up. I should say that the diff lever in the car works perfectly, it's in the rearward and to the right position for normal use and if it is placed to lock the diff's in low or high the light comes on every time. So in essence the transmission seems to slip in to a locked diff situation when it feels like it when all was okay in the evening at cease work but in the morning on start up the situation has changed.

Now in my retirement I got a little bored so I took a job delivering new and used Land Rovers from my local dealer to customers all over the UK - when I mentioned this problem to them this morning they looked at me as though I was mad but it is booked in for an inspection on the 2 June, but I know they won't find anything.

Any ideas?

jack one front wheel up and spin it ,if it wont its locked , turn the spigot on t/box with a 13mm spanner anti clockwise to release lock or clockwise to engage , selector it self is moved by the lever compressing a spring it may well be out of adjustment

Thanks James - between now and the inspection date I'm going to cut and paste all suggestions for the dealer to read.

Have you checked if the ABS sensors are sitting properly. I had nearly the same problem after changing the swifleball bearing. The problem was, that the teeth in the swiffleball there "round" and so the ABS sensor couldnÄt get a proper Signal. Finally the sensor caused that error.
But with warranty... let the LR dealer look for it.