Jet was not core to 9/2/65 selection of an MR Comet 4: Ministers made it clear to industry that a UK-solo MR would be bought, P-3/Atlantic simply disbarred, if a real fixed price was bid. CJG/Nimrod's Genesis gives us various C-130s/Vanguards/Britannias. Roy Jenkins, MoA, had secured access in Long Term Costings to the 1965-75 money liberated by the 10 year dwell before payments for the $ package (offered inc P-3C). Bids must fit into that slot, no later yelping for more. No constraint was to interfere with this money issue - so alms for Shorts would be nice, but not if that impacted price/time. RR, Spey variant, agreed with HSAL (Comet MR) to take a punt on a package fixed price. No other scheme was so offered, by RR, HSAL, or BAC. Basta! Fixed price contract 19/1/66, R&D+2 prototypes+38 Nimrod MR.1.
Jet was very core to 12/96 £2.2Bn. for BAe. to fit a GEC-Marconi suite in 21x(ex-MR2) Nimrod as MRA4. LORAL/Marshalls retread P-3A/B, v. new P-7 (Prime Contractor: GEC-Marconi) (and an Atlantique 2.5). The logic was accepted by Ministers that 21 retread Nimrods could be extracted from the existing fleet, such a happy fit with the fact that only with jet-fast transit to patrol station could "only" 21 provide Continuous Cover of the Gap, 1 a/c forward way up North, 1 closer to Kinloss, 24/7. The higher inventory of any turboprop platform would create higher long term cost of ownership: in 1996 people were learning to spell Integrated Logistics Management - Nimrod Majors at Kinloss had been civilianised 1/6/95 to FR SERCO: Long Term Partnership Agreements, Contracts for Availability were being brewed up by the Consultants.
Maybe that point of jet transit later influenced deletion of P-7 Super-Orion, insertion of P-8 for USN.