This is such a wooly area, differing in opinion is rife, I called FCL at Gatwick to ask what the score was. They said that if you were doing a test you can log it as P1/S. If you do a checkout flight with an examiner you can also log it as P1/S. They also seemed to believe that a 6 monthly, club rule, checkride could also be logged as P1/S, however LASORS say otherwise as this I think counts for regressive training. I logged my PPL skills test as P1/S which got through fine, and I had two six monthly checkrides with an examiner, who signed these off as P1/S. I did have 6 monthly checkrides with a bog standard instructor which I logged as PUT. Don't forget that your CPL skills test, if successful counts towards the 100 P1 hours as it can be logged as P1/S.
Purpose of my comments are that I think SRG are unclear on the situation too!