orca
Because its a T Mk 4 in the book (fit was 2x 100 gall tanks and 2 baggage pods). I've dug out my copy of the book and tried to work out how far the flight would have been from the references in the book. I reckon a low level phase one way of around 650-700km. Drops off the tanker over Norway in the area of Narvik, Low level over Norway with penetration crossings of Sweden and Finland airspace before crossing the Norwegian / Soviet boarder just south of Krikenes. Of course as soon as the Harrier was a reasonable distance back into NATO airspace, it could go high level, but that bit isn't covered in the book. Also the Harrier T4 were fitted with TFR according to the book.
Writers have no sense of distance.
The Extin pods were something that came along much later and at the time that the book was written, the GR5 was going to be a re-winged GR3 (1980).