Off the top of my head, I'd say the loss would be relieved as a Balancing Allowance. The loss on disposal of asset, which will be an expense in the P&L of the business, will be added back, as is always the case. IIRC you only get a wear & tear allowance when the asset is still owned and in use at the period end for the purpose of the trade. So what you have is an asset which has a tax written down value at date of disposal equal to its cost. The proceeds on disposal are less than this TWDV, so the difference is a balancing allowance.
That's purely off the top of my head, without referring to anything, so someone else might correct it if I'm incorrect...
I don't see why its any riskier than any other disposal of a vehicle, assuming there's a valid explanation for how/why they decided to sell a nearly new vehicle (plenty of businesses in recent times may have been forced to do so for cash flow reasons).