It's all spelled out in LASORS. See Section C6.2.
Note that where it states, for example, '20 hours of dual instruction with an instructor authorised under JAR-FCL', that does NOT mean an additional 20 hours!
The solo cross-country time stipulated means precisely what it says. So, even though a NPPL permits you to fly with passengers, you must fly the 150nm QX-C alone and unassisted and must be supervised by a JAR-FCL FI.
If you've already passed all the NPPL exams, you don't have to take any others. But if you had certain waivers (e.g. as a service navigator/observer) at NPPL level, you'll have to take those exams.