It depends on what the instructor wants to do, there is no requirement for the time to be logged as P/UT since there isn't any training going on.
As an instructor I usually put this down as P1 and the person being checked out as P/UT, it cannot be P1/S. This is due to the fact that I am actually in overall command,(after talking to a chap from the CAA and having it explained to me that they would always consider an FI to be in command, even if they were sitiing in the back on a jolly, in the case of an accident/incident.)
If the checkout in a new machine DID include new technology, i.e VP prop, Rectractable gear, Turbocharger or pressurisation then the flight must be as P/UT, but if it is just a check out in another SEP type, then it can be P1 if you negotiate and the FI is feeling generous! For the first few flights in any new type, most people are behind the ball and so there is usually no argument about putting it down as P/UT as training will often be needed, rather than the FI sitting there twiddling their thumbs.
I don't know why people worry about what to put stuff down as. It's not as if it matters to the average PPL what it goes down in the book as.