Ok I see thank you for explaining. There is a distinction here between civil and criminal law. The criminal aspect would be him being over the limit so that is a separate offence and him crashing the car and causing injury is a civil matter. I will only address the civil matter.
As a named driver on the policy, the first point to note is that he was insured to drive the vehicle. This means any accidents whether by fault or non fault would automatically be dealt with by the insurance company of the vehicle. So the third party whiplash claim would come off the insurance policy and you as the policy holder who permitted and named your son as a named driver would be affected, when it comes to renewals or premiums etc. Your son no doubt would also be affected if say in future he had to get his own insurance as he would have to disclose these details, but for now as you are the policy holder it will be your insurance that is affected and therefore your insurance company will cover the cost of the claim for the whiplash injury and any property damage like the empty car.
However saying this, there is actually a defence to be used if the third party did put in a whiplash claim. So please make sure your insurance company investigates this before agreeing to any payments. The leading case for this is Owens v Brimmel  you can google it to get a brief outline. But it essentially states if a passenger gets into a car with a drunk driver and knows the driver is drunk, then his damages for personal injury will be reduced by 20% as he has negligently contributed to it.
There is also the common law doctrine called “Volenti Non fit injuria”. This basically states that where someone has willingly placed themselves in a position where harm might result, knowing that some degree of harm might result, they are not able to bring a claim against the other party. So if this injured third party knowingly placed himself in the vehicle of a drunk driver he may not be able to claim at all. And if this can be proven, then no money will be paid for his personal injury. Of course this all depends on the results of the blood test. But your insurance company should be able to investigate this further.
I hope I have assisted you today. Please take a moment to provide a positive rating for me by clicking the stars above. I would be really grateful. And feel free to ask any further questions at no extra cost. Kind regards, John.