I'm going to stick my neck out here and say that if a search hasn't appeared in Experian (I think they are the same as Clearscore) then PP probably haven't done one. (although it can take a while to show).
Most of the big six do searches (possibly EDF don't or didn't). The main thing they look for is default with an energy supplier, I don't think just having a bad score would necessarily preclude you.
Obviously if you persistently don't pay you'd probably end up with a naughty mark on your file.
There is a little less reason for PP to do one because the first payment is made when you switch, so technically I guess you're paying up-front- I'm not sure if that is still considered to be credit?
It's really down to @Nataly
to answer this one.
May I ask why you asked?