Yes you may, however, only diesel generators are permitted and they must be silenced.

In addition to this you must have a powder Fire extinguisher to hand.

The generator must be located out of reach of the public, the output must have residual current protection and installation and operation is to be within the manufacturers guidelines.

Prior to use you must obtain a certification tag from festival organisers, who will require sight of manufacturers documentation and will ensure your fire extinguisher is within date.