If a vehicle has no insurance but you have fully comprehensive cover on another is the non insured covered to be driven?

It depends on the specific terms and conditions of your comprehensive insurance policy, but in general, non-insured drivers are not usually covered to drive any vehicles, regardless of whether you have fully comprehensive cover on another vehicle. Comprehensive insurance typically only provides coverage for damages caused to your own vehicle, and in most cases, it will not extend coverage to other vehicles or drivers who do not have their own insurance. You should carefully read your insurance policy and consult with your insurance provider to understand the exact coverage provided and the eligibility of non-insured drivers.