If the OP is booking NCL-LHR-Europe-LHR-NCL it is extremely unlikely he will be offered a POUG. These are usually offered only on itineraries from LHR/LGW/LCY.

It's also not wise to rely on mysterious POUGs which may or may not appear anyway if the TPs are essential.

The answer is to book in the class that you want to travel in, and if that includes a Saturday night, then so be it.