Foreign secretary Philip Hammond has said he didn't "see the need" to make contingency plans for a Brexit vote.
He dismissed concerns over the government's failure to plan for Britain leaving the European Union, saying the process could take years.
And he said that if the government had made plans and they had leaked, it would have been "seen as an unwarranted intervention" in the referendum campaign.
Britain voted to leave the EU by 52% to 48% last month. David Cameron is stepping down in September and has said it will be up to the next prime minister to trigger the formal process of withdrawal, known as Article 50 of the Lisbon Treaty.
Appearing before the foreign affairs select committee on Thursday, Hammond – who campaigned for Britain to stay in the EU – was asked why no contingency plans for Brexit had been made.
He replied: "I’m not sure that I see the need. The decision that has been made will be implemented over a timescale that runs into years.
"Its clear that an Article 50 notice … will not be served immediately. That will be done over the course of a period of time running into months."
Committee chair Crispin Blunt, a Tory MP, said the government had simply ended up delaying Britain's exit from the EU by giving the civil service an "instruction to do nothing".
Hammond said: "Throughout the referendum campaign, I drew attention – as did others in the campaign – to the likely consequences of a Leave vote and the reaction that I heard was that this was scaremongering.
"I think if we had sought to engage departments of state in preparing evidence of the likely consequences of a Leave vote and that information had found its way into the public domain, that would have been seen as an unwarranted intervention in the course of the campaign."
But Blunt pointed out that Whitehall always prepared for different outcomes at a general election.
"The government, for political reasons, appears to have taken a decision to place the country in a place where there was no contingency plan for the Leave vote, outside of the financial markets," Blunt said.
"This is a serious oversight in terms of the critical path in understanding what the issues are that the country’s facing."
Hammond said it wasn't up to "the government alone" to make contingency plans – because Britain's future depended on what could be agreed with the 27 other EU nations.
"So that uncertainty will be there until agreement is reached," he said. "And I don’t think the government having a clear but unilateral position as to what it would likely be would have changed that situation."
He added that it would be "very unwise to lay all our cards on the table for our negotiating partners to see".
Hammond also came under fire over his reluctance to guarantee that the 3 million EU citizens living in Britain could stay in the wake of Brexit. He said the UK could not do with this without an assurance from other EU nations that Britons living there would also have their rights protected.
Blunt said this position was "wholly misconceived" because negotiations could take years and people needed reassuring now. "I have to say your attitude strikes me as ‘I told you so’," he said.
Hammond denied it would take years to sort out, saying talks on the status of migrants should happen early. "The rights of people are deeply linked to the way our future relationship works," he said. "I would hope that we will focus early in the process on agreeing the big elements of the package."
Tory MP John Baron said this wasn't good enough and that the government's "predominant message is that EU nationals are being used as a bargaining chip".
But Hammond rejected that: "I have said that it is the government’s intention and desire that we will be able to establish on a reciprocal basis the rights for those people who at 23 June were either EU nationals living in the UK or UK nationals living in the EU to carry on exactly as they were. That should be our objective."