One of the many incorrect predictions about this year’s referendum was that those who voted for Brexit would soon regret it. The theory was that these deluded souls only intended to lodge a protest vote, and would be overcome with buyers’ remorse as Britain fell headlong into a deep recession.

Two months after the referendum, there is precious little regret. Polls suggest that just 5 per cent of those who backed Brexit wish they hadn’t; the same is true for those who voted Remain. However, the Remainers have moved quickly and effectively into post-campaign mode and have found a new vocabulary. Their new enemy is ‘hard Brexit’. They seize on every piece of bad economic news while rubbishing renegotiation prospects. They work effectively through agencies such as the Resolution Foundation, now perhaps the most influential think tank on the left.

And from the Brexiteers? Silence. We have barely heard a squeak from Vote Leave since the referendum. The group, like David Cameron, seems not to have had a plan for its victory. Like athletes collapsing at the finish line, they threw every last bit of thought and energy into the campaign and saved none for its aftermath. As a result, the side who won the war now risk losing the peace.

With Vote Leave gone, Brexit risks being defined by its enemies and moulded to fit their caricature. Theresa May, for example, has adopted a fringe position on EU migrants, keeping open the possibility of deporting them en masse in the confused belief that, if she doesn’t keep up that threat, British pensioners might be expelled from the Costa del Sol. Vote Leave had said all EU nationals here legally should stay legally, a consensus backed by everyone from the Liberal Democrats to Ukip. But when Mrs May decided to place a question mark on the status of legal EU passport holders in the UK, Vote Leave was not around to show her the consequences.

They can be seen now. Employers say their EU staff are alarmed, and worried that they are no longer welcome; some investors are pulling out because of the uncertainty. This week, hospitals warned that EU doctors have started to leave the NHS. The damage is serious. With so few voices defending the Brexit vote, more errors like this seem certain.

Mrs May shrewdly appointed Brexit-eers to positions of influence in the government, but this already looks like turning into a bad episode of Yes, Minister. David Davis, the Secretary of State for Brexit, was handed a new government department only to find himself fighting a one-man turf war with the civil service. Permanent secretaries are boasting about how they have stopped their most talented officials being seconded to help the Brexit agenda they campaigned against. Mr Davis had hoped for a team of 200 people to help chart the new territory; he has been given 100.

Jeremy Heywood, the chief mandarin, likes referring to ‘the current Prime Minister’, a reminder that he has now served four. Elections and referendums come and go; he still runs the government.

How do you bring about change if the government machine is opposed to your agenda? Margaret Thatcher faced a similar predicament when she became Conservative leader, inheriting a party apparatus that had become part of the failed collectivist consensus she sought to overthrow. She needed a new organisation to kindle new ideas, and looked to the Centre for Policy Studies. This model, that of the external think tank, has since become common. When he was education secretary, Michael Gove used the New Schools Network to develop his free-school project; Iain Duncan Smith used the Centre for Social Justice for his pioneering welfare reform.

The recipe for changing anything in the UK government is simple: ideas come first, action second, and a close relationship must be maintained between the two. It’s encouraging to see that Matthew Elliott, who jointly ran Vote Leave, reviving Business for Britain. But reinforcements are needed. Think tanks, websites and other groups should make the case for the clear, open version of Brexit that was described, and endorsed, at the referendum. Michael Gove did more than perhaps anyone to make the case for Brexit and widen its appeal. Theresa May has said that she does not require his services in her government, which leaves him at a loose end. He once set up a think tank, Policy Exchange, which went on to be an incubator of extraordinary talent. He could set up a new one now, providing an intellectual leadership that will not come from any government department.

As Charles Moore observed recently, the Brexiteers still seem unable to recover from their victory, like Bonnie Prince Charlie’s Jacobites reaching Derby. The referendum was just one battle, but many more now follow. The vision of Brexit sold in the campaign was detailed, liberal, globally minded and massively popular. It’s time to start fighting for it once again.