Bit of an update - I got my car back earlier today, not fixed... What they said was :
The sensors are both fine - not broken, no split or missing wires and all plugged in
The stepper motors both seem to be working, and it would be very, very unusual for them both to go at once, but...
The fault codes they are seeing are inconsistent - sometimes it throws up the sensors, sometimes the motors, sometimes a fault indicating water, and sometimes everything.
They also said that the fault is intermittent - even plugged into their diagnosis machine that can re-set the LCM immediately, sometimes the lights level and sometimes they don't. Conclusion - LCM most likely buggered. Which isn't ace, because it's a £4-500 part
However, they're a sensible bunch and before they go ordering a new LCM they want to check everything else, meaning bumper off and lights out etc., which they didn't have time to do today as I needed the car back mid-afternoon. So, it's booked in the day we get back from holiday so they can have it overnight as I need it fixed for the following week and our trip to Scotland. Which means that after 2+ weeks without using it, the first place I will drive is straight to the garage, which I think sucks as much as (if not more than) the potential bill. Shite :x