Cameron and Osborne have been savaged by MPs for their handling of last year's Brexit referendum
Then Prime Minister Mr Cameron staged the vote in the first place to call his critics' "bluff" and there was no proper planning for a Leave vote, said an authoritative Commons committee.
He then failed to take responsibility for the result, choosing to quit when his preferred Remain campaign lost although he had said he would carry on.
The MPs highlighted then Chancellor Osborne's use of so-called Project Fear tactics to try to scare voters into staying in the European Union with doom-laden and over-confident claims about how it would hit their pockets.
The Government's £9.3million outlay on a pro-Remain leaflet to every home in the land was also singled out for condemnation by the Public Administration and Constitutional Affairs Committee in its inquiry into lessons for future referendums.
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The Government was against the suggested proposal, the consequences were less clear, and the Prime Minister of the day would not implement the outcome
The MPs said last June's vote was an example of "what might be called a 'bluff call' referendum in order to close down unwelcome debate.
"The Government was against the suggested proposal, the consequences were less clear, and the Prime Minister of the day would not implement the outcome.
"There was no proper planning for a Leave vote so the EU referendum opened up much new controversy and left the Prime Minister's credibility destroyed."
They were scathing about Mr Cameron's ban on formal contingency planning for a Brexit vote – although civil servants had done some preparation including at an "away day … held without the Prime Minister's knowledge".
In future referendums officials should be expected to prepare for both possible outcomes
In future referendums, officials should be expected to prepare for both possible outcomes, said the report.
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"It should be reasonable to presume that the sitting Prime Minister and his/her administration will continue in office and take responsibility for the referendum result in either eventuality.
"A more responsible conduct of the Government’s case in the run up to the referendum, and proper planning for a Leave vote, would not have opened up so much new controversy nor left the Prime Minister's authority and credibility undermined."
It was a "questionable" use of referendums to call one to shut down debate, stressed the MPs: "Indeed, it is incumbent on future Parliaments and governments to consider the potential consequences of promising referendums, particularly when, as a result, they may be expected to implement an outcome that they opposed."
Given the lack of agreement about what a Leave vote would actually mean, the Government should have made more effort to explain and thus plan for either result, but had clearly not wanted to engage in the impartial consideration that would have entailed.
Ministers should also have heeded previous calls to clarify officials' roles in such campaigns, because there were times "when it appeared to many that civil servants were being drawn into referendum controversy", added the MPs.
"This damaged the reputations of the Civil and Diplomatic Services for impartiality."
The committee noted criticism by witnesses that while Treasury analyses of the potential impact of Brexit were couched in "relatively sober terms", Remain campaigners including Chancellor Osborne had discarded caution to allege that Brexit would make every household £4,300 worse off and trigger recession.
David Cameron stands down as MP Mon, September 12, 2016
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Prime Minister David Cameron with his wife Samantha leave 10 Downing Street for the last time after speaking to the press to visit Buckingham Palace to formally tender his resignation to the Queen on July 13, 2016
The committee said: "The Government was legally obliged to publish reports on aspects of the UK's membership of the EU.
"However, the presentation of these reports, particularly those from the Treasury, and the decision to spend £9.3million on sending a leaflet, advocating a Remain vote, to all UK households, were inappropriate and counterproductive for the Government."
Governments could legitimately take official positions in referendums but fairness relied on "careful and restrained" use of their institutions.
"Unfortunately, many of the Government's actions in the run-up to the referendum appear to have increased public distrust."
The Government should have made more effort to explain and plan for either result
The crash of a key voter registration website in the run-up to the referendum may have been the result of a foreign cyber attack, the committee said.
The Government blamed last June's crash of the site hours before the deadline for people to sign up to vote in the referendum on an exceptional spike in demand.
But the committee added: "We do not rule out the possibility that there was foreign interference in the EU referendum caused by a DDOS (distributed denial of service attack) using botnets, though we do not believe that any such interference had any material effect on the outcome of the EU referendum."
It urged the Government to extend its thinking about "cyber" security to beyond the purely technical and computer-based definition.
Its work should include how Russia and China use an "understanding of mass psychology and of how to exploit individuals" to influence public opinion, they said.