Who does bernard appeal to for permission to bring linda and john back into civilization? why is he granted permission?

Bernard appeals to Mustapha Mond for permission to bring John and Linda to London. He receives permission because the two, particularly John, are of scientific interest.  

"I ventured to think," stammered Bernard, "that your fordship might find the matter of sufficient scientific interest …"

"Yes, I do find it of sufficient scientific interest," said the deep voice. "Bring these two individuals back to London with you."

"Your fordship is aware that I shall need a special permit …"

"The necessary orders," said Mustapha Mond, "are being sent to the Warden of the Reservation at this moment. You will proceed at once to the Warden's Office. Good-morning, Mr. Marx."

i dont know sorry why dont you looking it up on google