If you jack up the wheel you had hanging with the others on the ground if it turn freely and the prop stays still the driveshaft is out.
Well that was a bloody weird one. And I either understand what happened, or am racking my brain trying to make sense of it.
So- it's working again, and here's what I did:
- jacked up each wheel at a time to check the axles as you said- both engaged and working fine, but I noticed a slight wheel camber which I'd just thought it needed to adjust itself whilst moving.
-after I did that, I jacked the whole front end and just let the car shift itself back straight.
-jacked the rear end up hap-hazardly (on an uneven hill) and let that shift itself to match, then belted the wheels and gave the callipers a tap to free them off.
- got in it, and she lives- back and forward a few times in all 3 height modes and all's well.
My guess is, by being on uneven ground while jacking when I've out the wheels on its somehow sat itself at a funny angle, pushing the driveshafts in/out causing them not to engage while the camber was out, so by jacking the car and thinking f@ck it let it slip- it's straightened itself out and is now happy and ready to ride the tarmac once more.
That, or with the brakes seized on it was protecting itself by not throwing everything it had at them
Anyway- all sorted and head scratching can conclude.
Thank you for your help everyone, sorry I'm a total moron!