As the original post asked about SEP (or SSEA as it is now) I assumed that's what we were talking about and didn't think that we might be off on microlights or anything else.
I'm only a humble NPPL myself and there is a lot of much more accurate information out there but as I understand it:
NPPL is split into three main groups
SSEA - Light aircraft to me and you - You can fly anywhere in the UK in reasonable weather, during the day with up to three passengers - none of whom need to hold your hand or be qualified astronauts or anything.
You can fly aeroplanes with the spare wheel at the front or the back, you can fly ones without any wheels but with floats or skids, you can fly ones where you hide the wheels while you're flying and hope to remember to retrieve them from their hiding place before you land. You can fly aeroplanes where the props all wobbly. In fact you can do most things you'd ever want to do, just not in clouds or with more than four on board.
SLMG - You can do much the same (probably not as many pax, though) in gliders that have engines to launch themselves; in fact you can probably do much more.
M - You can fly microlights and probably to far more places but...
...as I said, I've got the first type and assumed that that was the topic.
Now, I've heard that pilots with NPPLs look just like ordinary pilots but at night they turn into badgers and feed on oranges and beetles; is this true or just a rumour?