The original letter is in the Perfin Society Library
The text of the letter is as follows:
General Post Office.
13th March, 1868.
The Postmaster General has had under consideration your letter of the 27th ultimo, and His Grace desires me to inform you that, under the circumstances, he will not object to the perforation of postage stamps in the manner described by you, with a view to protect merchants and others, as far as possible, from the theft of the stamps used by them.
I am, Sir,
Your obedient servant,