The comment about a guilty plea potentially being tantamount to perverting the course of justice came from a previous poster. I probably misunderstood but basically trying to enter mitigating factors in the hopes of the court converting a guilty plea to not guilty could be viewed as an attempt to pervert the course of justice.
Whilst I would not argue with Andy's interpretation of the law (he knows much more about these things than I do) personally I doubt that would happen to an unrepresented defendant in a Magistrates' Court. A defendant representing himself is not expected to know such points of law and whilst a guilty plea for the sake of expediency is often refused by a court, I would think the worst that would happen would be just that.
There is a defence to the charge which says this:
“the person on whom the notice is served shall not be guilty of an offence under this section if he shows either that he gave the information as soon as reasonably practicable after the end of that period or that it has not been reasonably practicable for him to give it.”It was not “reasonably practicable” for your husband to give the information within the time allowed as he had not received the request by the time that period had expired. However, he gave the information as soon as it was reasonably practicable for him to do so (i.e. as soon as he received the request).
The task he will have is convincing the court that the request was not received in time. You do seem to have quite catalogue of reasons why your post may well suffer problems. If he does decide to defend the charge it would certainly be beneficial If he could provide some independent evidence of this, perhaps from neighbours or even the Post Office.
In the event he decides to plead guilty it is unlikely that any mitigation will significantly influence the sentence. The offence carries a fixed six points and the level of the fine is fairly prescriptive. So I think really the decision is whether to plead not guilty and trying to convince he court that the request was received late, or to plead guilty and get the guaranteed reduction in the financial penalty that comes with that.
This is a life changing event and I am devastated.
Of course I don't know your personal circumstances but I imagine there are few people for whom this would prove to be a "life changing event". Whilst it is not the least serious of traffic offences, it is fairly minor in the scheme of things and attracts just a fine and penalty points, though you will see quite an increase in insurance premiums for a few years. How else do you suspect it will change your lives?