I second that, but I would also make a complaint about the police's handling of it. They over-rely on the insurance database which is a computerised entity and can and does contain errors...people who are legally insured but not on it, and people who have no insurance who mistakenly are on it. The police know this full well, but as they don't give a toss about the truth but only about convicting people whether or not they're actually guilty, they're not going to question what the insurance database says, that could mean crucial lost revenue in fines.
When the son produced the insurance documents at the station and the database still returned a negative, the police should then have rung the insurance company direct, and spoken to a human to confirm that the guy WAS insured. It could have very easily been dealt with at the time but the police chose not to do this as it would have reduced their chances of nailing him on some sort of offence.
Based on that I would make a complaint to the local Police Authority and then to the IPCC if the result is not satisfactory. The police is an institution full of corruption and rogues who are just as bad as the criminals they go after, they are not interested in justice or the truth, just money and convictions of anyone they come across regardless of guilt or intention. They do not know the meaning of the words discretion or common sense. They are institutionally racist (this is a fact, declared by numerous judges) and apparently ageist too. There are bad drivers of all ages, there is no reason to single out the young. Do your bit in getting back at these dreadul people who are the pits of our society.