Learner drivers (people on their Ls) will not need to get a separate car insurance. As long as there is a listed driver in the car, they are automatically covered under the listed driver's Bingle insurance policy.
The learner driver will then be treated as a listed driver, and an additional age excess will apply if they are under the age of 25 at the time of the incident. Once the learner driver is on their Ps you may want to list them as a driver on your policy. Otherwise an unlisted driver excess might apply.