Conspirators are contemplators after the event, often looking for an angle to sell their scrawl. It's human to regret...not the cancellation, but the squander. Take M.52, prime example of conspiracy...? The decision to fund it (Oct.43) was made by a Minister (RS Cripps), advised by officials. Time, money efflux, things change, we discover swept wings, we decide "Miles was very good at biffing out cardboard aircraft but had never done (something this complex)" M.Morgan, D/Director RAE. Egg on face, not caused by chop, but the folly of ever funding it at all. So it's Feb.1946: Peace; no requirement for military experiments. Then-junior official Lockspeiser is now senior; then junior Minister is now in Cabinet, with future bright prospects as Trade Minister...except that UK is skint. Who volunteers to tell him we boobed, and should have chopped the thing long ago, when we grasped it would serve no purpose. So we wait till Treasury cuts the total budget, then look for the least painful sacrifice. Or, VC7/V.1000 "worst blunder of all" said...oh, the builder: well he would, wouldn't he? Initiated in Korean scramble, 1952; Transport needs differ by 1956. The Minister chopped it "because I couldn't find a customer. BOAC didn't want it and RAF couldn't afford it" (MoS R.Maudling, Memoirs). Once the decision to chop is taken, Ministers' obligation to us, the taxpayers, is to get out cheapest, quickest. Keeping data/tools intact is necrophilia: cost is not mere drawer-store, but calibration, load-path currency - warmware. See the costs of answering today for Continued Airworthiness of DH/Auster/BEAGLE types and parts. If some future Minister thinks to resurrect the cadaver...the Zombie would differ top to toe, due to obsolescence of the tangible (there is a ludicrous assertion that Maggie's lot in 1979 contemplated grave-digging the 1959-defined TSR.2. Well, we did Wapiti the DH.9, but really....)
I know of no cancelled project that can warrant any regret other than the delay in doing it.