For The Love Of Port

Any other books out there that are "must have's"? These may or may not be "must haves" but with regard to Port they are both interesting and informative and I'm glad I have them: The Factory House at Oporto ... John Delaforce, 1979, ISBN 0 903 432 17 X Port ... George Robertson,...

... at least to me!

Does anyone have experience of or information about Niepoort Petre's Port?