Nice to see I'm in demand. And for the record, I'm a tatooed male with a skinhead and comedy moustache (rarely mistaken for the female of the species!).
I think Woozer has hit it on the head - if your son doesn't have legal expenses cover, then the best option is to contact a company such as Albany, or DAS Legal Expenses, and they should (hopefully) provide him with a hire car for the duration of the case.
They would normally also arrange for an engineer to see his car, arrange repairs where applicable, but will stop short of actually paying for the total loss of the vehicle.
They would also take care of the personal effects, etc (uninsured losses).
HOWEVER, as has been pointed out, if there is any sort of issue (i.e. drink or drugs), then there may be issues over the other insurers paying out - they'd still have to long term, but they may drag it out due to investigations, etc.
If you do have the other guy's registration, I'm happy to run a search for the insurers