No Insurance is an "absolute" offence. You either have it or you do not. It is your responsibility (absolutely) to ensure you have it and you did not do so.
Ask your solicitor (who seems to know about these things) to take the case on for you and plead not guilty in the magistrates' court. You will almost certainly be found guilty at trial. You will be fined one and a half week's net income, and about �450 costs and receive six penalty points. And, of course you will need to pay your solicitor his fees.
You could reduce the fine and costs considerably by pleading guilty, and offer your mitigation, but you will still get six points.