(Grateful for this interesting point made by Trevor Gilson in a recent letter).
According to my local council, the session requires a PEL because there are more than two 'performers'. This they say is to ensure the public's safety and interests.
Should Robbie Williams and Brittany Spears form a duo and 'perform' in the same place? A PEL would not be required as there would be only two performers.
The then REAL issue of public safety would have to be dealt with the other, already exsisting legislation.
The very same legislation that already ensures public safety for the members of the public at the session without a PEL.