As it stands, motorway lessons are not compulsory. Once you pass your practical driving test, you are automatically entitled to drive on the motorway. However, as a learner you are barred from driving on the motorway.
This is potentially problematic since a driver with no experience on the motorway at all, having not been taught motorway driving, can freely drive on the motorway. This leads to motorists developing various bad habits such as tailgating and middle-lane hogging as they have never been taught how to drive on the motorway properly.
However, this is voluntary and there is no requirement that newly qualified drivers take motorway lessons.
There are calls for motorway lessons to be compulsory with the government announcing plans to let learner drives use motorways in 2012 provided they were accompanied by a qualified instructor. However, to date, there is no sign of this law yet being implemented. There are also practical problems in including motorways in the driving test, in particular, with individuals who live nowhere near a motorway and so would having experience of the motorway let along including it in their test.