Newly qualified drivers can take Pass Plus — a voluntary course that covers motorways, dual carriageways, town, night, and weather. Some insurers offer a discount; ask before you buy. You do not have to take it, and it is not a second test.
You can drive on motorways as soon as you have a full licence. If your instructor offers a post-test motorway session in a dual-controlled car, it is one of the better pounds you can spend.