"Aren't they then driving without insurance? All the named drivers will have had to sign the consent form when the insurance was taken out."
No.
Any licensed driver who does not live with you and does not regularly and often drive the vehicle who drives the vehicle with your permission is covered by the insurance.
Any person who lives with you and is listed on the insurance policy as an additional driver does not need to sign anything.
Biting the hand that feeds IT
