Just to explain that the Statutory Declaration does not put the matter to rest. All it does is to formally inform the court that your OH knew nothing of the proceedings which took place in his absence and at which he was convicted. Your OH will have to ask the court to re-open the case and to “set aside” the original conviction (which effectively treats it as if it never happened). What happens next is that he must formally enter a “not guilty” plea. After a case management hearing (which may be held on the same day as the plea is entered) the matter will be listed for trial.
It is certainly true that the burden of proof rests with the prosecution. They have evidence to support the commission of the offence and they have papers which purport to have been completed by your OH admitting he was the driver. This should be sufficient, without a defence being entered, to achieve a conviction (and indeed it did at the original hearing).
The burden thus shifts to your OH to refute the allegations. He has a two pronged defence. Firstly he should be able to show that he did not complete those papers. Secondly he can show that he could not have been in the locality at the time of the allegation. (Obviously if the first is successful, the second need not follow). The level of proof he is required to achieve is not “beyond reasonable doubt” but on the much lower “balance of probabilities” (That is, his version of events is more likely to be true than not).
However, as Eddie has made clear, this is quite a complex matter and ideally a solicitor should present the case on his behalf. In fact, a lawyer may well argue that since your OH knew nothing of the proceedings he also knew nothing of the request for the driver’s details, had not supplied them, and so the prosecution cannot be sure they have the right person before the court.