Ward-minter is quite correct in saying that there is a difference in admitting guilt by way of accepting a fixed penalty, and being convicted in court (either by pleading guilty or being found guilty following a trial). One fundamental difference for the pedants amongst us is that a fixed penalty is not a fine and does not lead to a conviction � only courts can impose fines and register convictions. Nonetheless, the effect on the miscreant is the same.
If, in the example mentioned, the accused declines an offer of a fixed penalty and decides to plead not guilty in court, the magistrates would have to decide if an offence has been committed at all, and if so, whether there a reasonable defence to its commission which would allow them to reach a verdict of not guilty. As with all matters legal this is not as straightforward as many believe it ought to be. I would not say with any degree of certainty that �there is not a magistrate in the land who would convict�. To give you some idea of the sort of argument that might be faced, if the defendant used the excuse suggested by ward-minter that he thought life was being saved by him jumping the lights, he would be asked to show how he arrived at such an assumption. After all, he simply saw a police car and it may have been racing back to the Nick before the chips got cold! Flippant, I know, but an illustration of what might be faced.
This uncertainty, coupled with the prospect of a considerably higher penalty and being forced to pay a contribution towards the prosecution costs of the trial, deter many people from contesting what is often a reasonably arguable case.
The sad thing about this question is that it should have to be raised at all. It is not that long ago that common sense would prevail over simple legalities and there would be no chance at all that such a case would even be before the court, let alone any prospect that a conviction would result. Alas, this is not