If you are accused of driving without insurance, or causing or permitting another to do so, the burden of proof that insurance cover was in place rests upon you. The most common defence is that valid insurance cover was in place. There is also, in certain circumstances, a statutory defence available to those asked to drive by their employer although you would have had to have been misled into believing that cover was in place. (It may be possible to argue that this defence would also apply to the self-employed as well as to the employed.) You can read about the ‘employment defence’ here.
Whether there is a credible defence to a no insurance charge and if so, what it is, will depend on an analysis of all of the facts of each particular case. This area of law can be complex so if you would like to know whether you have a credible defence we should be happy to advise you.