.....there is a black plastic assembly, a box with a cover held on by 2 bolts. What's under there, and what sort of fluid does it contain? Mine's leaking after the accident; haven't had time yet to undo the bolts and see, but need to make sure the repairers are aware.

Where abouts?

Could fuel filter? Under the rear passenger floor?

In the boot on the nearside is the nav and radio equipment - that should be all dry.

Brake fluid or petrol most likely.

Terrible picture but it's coming fro this compartment:

Click image to enlarge

The only fluid you might get off the suspensaion is condensate off the compressed air. Can't make the photo out.

Stick your finger in it and taste it or smell it. if its fuel or brake fluid you could easily tell but i'd say it was fuel, and maybe for a fuel burning heater(do you have one??) FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

The BiB at the scene did this and said it was salty!! It's water-like, not oily.

Rear washer maybe? not sure how the pipework for it routes... FFRR MY06 facelift With TDV8 Alloys Zeros/ATR's
Mantec Sump Guard, Rigid Load liner, MY10 BT upgrade.

Sp M dispenser. Eww better tell the BiB to break out the mouth wash.

Sorry couldn't resist.

Seriously though I would have thought you'd smell washer fluid?

Not sure what else it could be. Sorry