[Part Two]
It is true that the Hamiltons succeeded with this defence (I believe they said they were sharing the driving on a long journey). But success is not confined to the rich and famous. The law is the same for everybody and the argument is successfully used regularly, as oldhamfan�s link suggests. But as I said earlier, it needs to be properly put and a solicitor is the best person to do this.
Your point about self-incrimination has been covered many times by appeal. It finally went to the European Court of Human Rights in June 2007. In the case of O�Halloran vs the UK it was ruled that Registered Keepers of motor vehicles could lawfully be compelled to tell the police who was driving it on a particular occasion and that this �...did not destroy their right to remain silent and their privilege against self-incrimination.�
From your description of the situation, I believe you have a good chance of success, especially bearing in mind the delay in receiving the notification (to which the court will give a good bit of weight). The downside is that if you are not successful your wife will be awarded six points, be fined about one and a half week�s net income, pay prosecution costs of about �400, and pay a Victim Surcharge of �15. If one of you owns up to speeding it�s �60 and three points (provided that whoever owns up does not already have nine or more points and that the speed was not so excessive to be outside the fixed penalty guidelines � which is over 49 mph in a 30 zone).
My advice is to consult a solicitor (unfortunately you will not get Legal Aid), explain all the facts, and do whatever she or he recommends.
Hope all this helps.