There are a list of allowable expenses that revenue allow,a clamped car regardless of the background story or who it belonged to or who paid the fine,is not one of them.
If his car had been broken into and you had paid for damages,you couldnt expect that expense be written off.
I know of one individual who puts receipts you just would not believe against rental income,his telephone/broadband bills,photocopier,the cost of servicing his car(due to visiting rental properties)etc,pure loony tunes,all well and good til he get audited,you can put anything down,its self declaration however if audited,I definitely do not think you could stand over the clamping bill.