From the information we found, in the UK learners driving a car must hold a valid provisional licence. They must be supervised by someone at least 21 years old who holds a full EC/EEA licence for that type of car (automatic or manual) and has held one for at least three years.
When beginning to drive, one option to get experience for a learner is to drive a parent or guardian's car. If your son is a provisional licence holder, you would need to be present at all times when he is driving. In this situation, insurance cover must be in place. This would require your son to be named on the car's current policy. So as the parent, you would need to inform your insurance company about teaching your son to drive and they will probably require you to add him to the policy.
Sources that we check said that a person with a provisional license must have a valid insurance certificate covering them for third party liability. Before driving any vehicle, they should make sure that it has this coverage; even a person learning to drive must not drive a vehicle without insurance.
[Let CarInsurance.com help you find affordable auto insurance now.] As you are probably aware, any vehicle driven by a learner must display red L plates. In Wales, either red D plates, red L plates, or both, can be used. Plates must conform to legal specifications and must be clearly visible to others from in front of the vehicle and from behind. Plates should be removed or covered when not being driven by a learner. Remember that a qualified driver should not drive a car if L-plates are being displayed or he is committing an offence.
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A provisional licence requires the learner to be accompanied by another person in the passenger seat when they drive who (a) is over 21 years old, and (b) has passed their driving test and held a valid licence for at least 3 years.
You mentioned you had comprehensive coverage on your vehicle. Comprehensive cover in the UK includes the same level of protection as Third party fire and theft but in addition includes protection for your car against accidental damage. Third party car insurance is the bare minimum level of cover of car insurance required in the UK. This cover essentially protects third parties (pedestrians or drivers) so they do not lose out financially should you injure them, or cause damage to their vehicle (not your own car).
Follow this link for a quote for UK insurance coverage. | 
