Civil servants used the final weeks before Britain's referendum on membership of the European Union to do "a significant amount of thinking" about Brexit, cabinet secretary Sir Jeremy Heywood has said.
Before a general election, opposition politicians are granted meetings with the civil service to allow Whitehall to ensure that any new government can hit the ground running.
But in the run-up to the vote on EU membership, then-prime minister David Cameron instructed the civil service not to plan for Leave vote, a decision that has since attracted widespread criticism. Former UK Trade and Investment chief Sir Andrew Cahn told CSW last month that the lack of contingency planning was a "humiliation for this country".
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Heywood, head of the civil service, told MPs on Wednesday that officials had "not set out to produce a civil service version of what Brexit looks like" because there "wasn't an end state that we could plan against".
But he revealed that the 28-day "purdah" period before the vote – in which both sides of the campaign were legally prevented from drawing on the support of the civil service – was used by officials to "look at what was being said by people advocating Leave" and to think about the departmental changes that would be needed to make departure from the EU a reality.
Confirming that Cameron had imposed a "red line" on contact with Brexit campaigners, Heywood said: "He didn't want us talking to the Leave campaign and working out elaborate plans for what would happen in the event of a Leave vote, for sure."
"The prime minister didn't want us talking to the Leave campaign and working out elaborate plans for what would happen in the event of a Leave vote, for sure" – Cabinet secretary Sir Jeremy Heywood
"But did we actually use the time usefully to prepare facts, analysis, options that would subsequently become useful? Yes, of course we did. And that's why, from the period from June 24 onwards we've been working flat out – and not from a standing start – on the issues that now need to be addressed."
In the wake of the vote to leave, the Cabinet Office moved quickly to set up a dedicated unit on EU withdrawal. This was later upgraded to a full-blown Department for Exiting the European Union by new prime minister Theresa May.
Heywood said the 28-day period had been used for "thinking about the organisational changes" that the civil service would need to implement in order to start work on Brexit.
"The idea of creating a separate trade department for example, that was something that I discussed with my senior team," he said. "We had an away day to discuss those sort of issues, in addition to the sort of policy thinking that we started to do in our heads."
Describing the row over the lack of formal planning as an "odd debate", Heywood said "significant" work by the Treasury and Bank of England to plan for the immediate financial aftermath of a leave vote had helped to calm market jitters.
And he said Brexit analysis produced by the Treasury and Cabinet Office, published in the run-up to the vote, had proved "extremely valuable" in light of events.