Struggling to see how s. 101 MCA applies - the driver being insured is not an exemption to the offence - it removes the entire legal basis of the allegation.
Case law provides that driving without insurance is a reverse burden offence - it is very difficult for the prosecution to prove a negative, and should be trivial for the driver to prove that he was insured, so for that offence to be workable, there must be a reverse burden of proof.
However, you have been charged with permitting. I am not aware of any case law specifically on the burden of proof for permitting. Whilst it is entirely sensible to impose a reverse burden of proof on the driver to prove that he was insured, it does not necessarily follow that the same should hold true for the person charged with permitting.
Where this starts to make my head hurt is that nobody involved in the process believes that the person you are accused of permitting to drive without a licence or insurance was actually driving. This is what is known as a prosecution under s. 69 of the Ways and Means Act. They think that you have failed to name the driver. They think that you have perverted the course of justice and/or committed perjury, but proving it beyond any reasonable doubt would be somewhere between too difficult and impossible.
If convicted, you can expect 6 points and a hefty fine for the permitting no insurance offence,