Margaret Thatcher, that fiery icon of British conservatism, fervently wanted Britain to be part of the European Economic Community, the precursor to the European Union. In an Op-Ed published in 1975, she listed the benefits of remaining in the EEC: improved prospects for peace and security; access to the largest “trading and aiding unit in the world;" increased bargaining power with the rest of the world.

She noted the perils of withdrawing from the EEC: adverse effects on investment and jobs in the UK, uncertainty about the exchange rate. She called withdrawal a “leap in the dark.”

How things have changed.

Now, a Conservative government, headed by Boris Johnson, is racing to get Britain out of Europe. After several months of arduous negotiations with the European Union, and the ignominious fall of a Prime Minister (Theresa May), Britain is set to leave the EU on October 31.

What will be the manner of its departure?

Before May stepped down, she had agreed to a deal with Brussels on the terms of withdrawal. The U.K. would pay Brussels about $50 billion, an amount that includes Britain’s existing commitments to the EU budget. A hard border between Northern Ireland and the Republic of Ireland would be avoided (for the time being). There would be a mechanism to deal with British citizens living in the EU and EU citizens living in Britain. A transition period, possibly lasting till December 2020, would provide time for businesses and everyone else to adjust to the post-Brexit reality.

The problem is, the Withdrawal Agreement was never approved by parliament. Furthermore, Boris Johnson and his Cabinet—all hardcore Brexiters—are not inclined to accept the terms of the agreement. They say that a better deal can be negotiated. They will use the $50 billion payment as a bargaining chip to force Brussels to capitulate. What the pusillanimous May could not do, the hard-nosed Johnson will accomplish.

The European Commission, the body charged with conducting the Brexit talks, says this is sheer fantasy. The deal on the table is the best the U.K. will get: take it or leave it.

So, what next?

While Johnson still holds out the prospect of a better deal, he is preparing for a no-deal Brexit on October 31. Under this scenario, Britain crashes out of the EU, without the safety net of the Withdrawal Agreement. No transition period, no certainty about the border between the Irish republic and Northern Ireland, no agreement on the treatment of each other’s citizens.

The immediate effects of such an abrupt withdrawal would be striking. The EU is first and foremost a free-trade agreement, and as a member state, Britain can export its goods to the EU without having to pay any tariffs or face other impediments. Similarly for European goods entering Britain. But once membership ends, so does free trade, with both parties now subject to the rules of the World Trade Organization. British goods destined for France, Germany, Ireland, etc. will be subject to tariffs imposed by the EU, eroding their competitiveness in the large European market. The British government would also impose tariffs on French and German and Irish firms, making their goods more expensive for domestic consumers. Goods traveling through ports and borders will have to be inspected, likely causing long delays.

The U.K. government is aware of this, and is preparing to spend large sums to expedite the customs and regulatory checks. The government has set aside some $4 billion to deal with the no-deal Brexit outcome, but trucks are still expected to get stuck in long lines, disrupting traffic for miles leading to the ports and the Channel tunnel.

Johnson claims that once the EU’s shackles are removed, Britain will be able to set its own trade and immigration policies, and become a more consequential country in world affairs. President Trump has made no secret of his enthusiasm for the Brexit project, holding out the prospect of a quick trade agreement between the United States and the U.K.

But, as Thatcher noted four decades ago, Britain risks becoming diminished once it leaves Europe. Its bargaining power in crafting trade agreements will be attenuated, not strengthened. Its attractiveness as a destination for foreign investment will be reduced. Johnson may yet come to regret making the leap in the dark.

Sanjay Paul is assistant professor of economics at Elizabethtown College.