A learner driver under proper supervision from a qualified instructor, in a dual control car should not be a risk. Before test they can practise on roads at the national speed limit which is the same as a motorway. The instructor would be in the car with them, so they would not put themselves in danger by taking a poor driver on a motorway.
I do not know if an arbitary number of driving hours could be put on it? Like, it could only be considered only if the learner had completed 25 hour lessons, and then it was not compulsary (for the instructor to allow it).