The good news is that anyone driving your car is covered. But if they're not listed on the policy it just means you will need to pay an unlisted drivers excess and any other excesses that applies (like, if they’re under 25).
You can find your excess amounts here
You’ll then be presented a list of the policies under your name – select the one that you’d like to update.
This will take you to the policy summary page, select ‘Update my policy’ from green left hand menu.
You’ll then need to select 'Listed drivers', from there you can update the drivers on your policy.
Changes to your policy can also change the premium you pay. Once you've made the change, you'll be notified if there's a change in premium.