From June 4th 2018 you are allowed to drive on the motorway before passing the driving test. This is only legal if you are with an ADI (approved driving Instructor) and in a dual controlled car.
Driving on a motorway is not part of the driving test because only a fully qualified driving instructor can take pupils on the motorway. Driving test examiners, parents and trainee driving instructors must not take pupils on the motorway or they are breaking the law.
Motorways are actually quite easy to drive on so long as you understand some basic rules and have experience of driving at high speed.
Below are three videos showing me driving on motorways and teaching them to a pupil. Select the video you want by clicking the menu icon at the top left of the video box.