Caroline,
Glicazide can cause hypos, so you do need to inform DVLA if you are still on that. Its only if you are diet controlled, or on metformin, or byetta, or januvia or one of those that can't trigger a hypo, that you don't need to tell them.
You and Steve should both tell your car insurance company. As LJ says, they won't increase your premium, but if you don't tell them and you need to claim and they find out about the diabetes, then you have given them the perfect opportunity to refuse to pay a penny. It makes no difference to them whether diabetes had any bearing on the claim.
Not only will they not pay but you also won't get back the premiums you will have paid them for providing you with no cover! Believe me, I have worked in the past in the insurance industry and they employ a small army of loss adjusters whose job is to find ways of avoiding having to meet a claim!