If you haven’t bought dollars since the EU referendum, be prepared for a lighter wallet. Over the airport counter, £100 will today buy you just $128 (on 22 June, it was $146). If you’re heading to the Eurozone, it’s €114 (€130 in June). That’s because, ever since they saw Sunderland vote to leave the EU, currency traders have been dumping sterling.

Although some forex traders believe the pound will bottom out at $1.20, the pessimists are predicting parity: one pound buys you one dollar. And I think the pessimists are right. Because there is no situation in economics incapable of being made worse by the uncontrolled antics of politicians. And antics are what we’re getting.

Theresa May’s conveniently short walk to Downing Street is designed to combat the impression that nobody is in control. But without a major change in policy, we are still rudderless on a churning financial sea.

Consider the mechanics of British trade. We’ve been running a current account deficit of 7% – a historic high. That’s because we import more than we export, not just when it comes to goods but to services. For every pound spent in the UK on goods and services, 7p worth of foreign money has to arrive to make up the shortfall.

A falling pound should, under normal conditions, stimulate the flow of foreign money into Britain, because the stuff we sell is cheaper. But these are not normal times.

In order to stave off a post-Brexit recession, it’s likely that the Bank of England will have to cut interest rates to zero. Ever since 2008, the Bank has been keeping this move in reserve in case all else fails, like an ageing centre-forward thrown on in the last five minutes of extra time.But the impact of zero interest rates is to make investing in Britain less attractive. And if the big fat zero does not work, and Mark Carney has to print tens of billions of pounds to stimulate growth, then sterling will become even less attractive.

What “straight” economists worry about is stagflation. Here, the falling pound boosts the price of everything sourced globally – from a Starbucks cappuccino to a MacBook – while growth goes into reverse. What political economists worry about, however, is the absence of a plan. Or a leadership. Or whether the public has consented to be governed by an elite that no longer understands what it is doing.

There’s a good reason George Osborne did not ask the Treasury to design a contingency plan in case of Brexit. What he, or his successor, has to do flies in the face of 30 years of centre-right policy.

A logical contingency plan would say: if the electorate votes for Brexit, we stay in the EEA and accept everything the Europeans demand to do a quick deal. That includes free movement because (yes, George, remember this) our entire growth projection to 2020 depends on 1.1 million migrants arriving, on top of those already here.

Next, even as the shocks of exit hit us, we redesign the economy so it produces wealth in a different way. We slash taxes to boost inward investment, but we can’t cut spending any more. So we borrow like crazy, print money and spend everything we can trying to create capacity to grow long-term. And we wean ourselves off migration, upskilling the workforce, replacing low-wage jobs with machines. However, Britain has not done national-centric industrial policy since Michael Heseltine was in charge, and his policy did not work.

It’s clear that Osborne, Carney and the rest understand what needs to happen in the short-term. But in the longer term, Theresa May does not seem to have in her mind a picture of any alternative economic model around which Britain could stabilise. As for Labour, the person in charge of formulating a new industrial policy was supposed to be Angela Eagle, but she has other things on her mind at the moment.

The IMF’s economists predict the UK’s capacity to grow will slump by 4.5% by 2019 if Britain ends up outside the single market. This “capacity to grow” figure is the measure against which debt sustainability is judged.

The national debt, close to 84% of GDP now, was destined to fall under Osborne’s old austerity plan. But this is being jettisoned – again chaotically – as the neo-Thatcherites toy with promises of a £100bn spending spree. More likely is that our debt rises towards 100% of GDP, crushing the value of sterling even more.

The prospect of Britain turning into a post-global disaster zone is real. Andrea Leadsom’s decision to shortcircuit the leadership race is proof of just how real. Politicians of all sides need to grasp one idea urgently: that Brexit is a mandate to begin making economic policy in the national interest first. Under a working global system, what’s good for your trading partner is usually good for you, because the system feeds the upside back to you.

Once you’ve put a hole in the multilateral system – and Brexit does that – your competitiveness has to be defined differently. Competitiveness now is about: what hikes real wages? What boosts investment? What raises productivity? What expands the export sector? These questions all raise another one: who is going to do it?

In economies that successfully game the currency and export system, the answer is usually the state. The government shapes the economy ruthlessly to ensure that, as the currency depreciates, there is export capacity ready to grow; and it relentlessly games the global trade rules.

This is called “neo-mercantilism”, as practised by Germany, Japan, South Korea and China. But it has not been the British way since Harold Wilson.

Instead, we are in the phase of flamboyant dice throws – Leadsom’s case shows how ill-advised these can be. The more I watch this circus, the more it becomes obvious that – in their subconscious – the political elites of Britain do not really believe we are going to leave the EU.

The total absence of engagement with the question “What is our future economic model?” belies the assumption that Mischon de Reya will stop Brexit with a legal challenge. They won’t.