Chris Gibson's book Nimrod's genesis would be the most reliable source, but a paper given to the RAF Historical Society includes a lot of mateiral provided by him.
It seems that there was no specific requirement for a jet aircraft. Air Staff Requirement 381, issued in 1964, called for a patrol time of 5 hours 1000 miles from base, with a transit speed of 300 knots. The Orion could not accept British sonobuoys, but a number of British proposals (including maritime version of the Trident, Belfast, VC 10, BAC 111, Vanguard and two Comet-based proposals) were assessed using the Breguet Atlantic as a yardstick.
Interestingly, a speaker at the same RAFHS seminar mentioned that "the propellers of a P-3 or an Atlantic produced a harmonic that the submarines could detect and identify from several miles away" whereas jet aircraft were less detectable.