What kind of Britain will emerge from the Brexit earthquake? Will it still be united? What role could it play in Europe and the world? Nobody knows the answers. But you can at least make plausible assumptions. One conclusion seems to be clear: The United Kingdom, which the world believed it knew – stable, pragmatic and respected – was gone forever. Lost reputations are not easily regained.

The most important change is in the political leadership. Boris Johnson, at best a serial fighter, will most likely become prime minister. The leader of the opposition is Jeremy Corbyn, a man whose lifelong passion is left-wing, anti-American politics. The dominant force in the country is Nigel Farage – a talented demagogue consumed by aversion to the EU. This is not a cast of protagonists for a country with a stable and mature democracy.

Then there is the danger of a no-deal Brexit. A parliament that allegedly wanted to leave the EU three times rejected the only deal that Prime Minister Theresa May – at least one adult – could reach. The Tory Eurosceptics were allegedly an opposition to the Irish backstop. However, they insist that this hard-line prevention plan is not necessary in Ireland.

In any case, this would only prevent Britain from concluding trade agreements that are less important than maintaining good relations with the EU, which are likely to be unavailable (as with China and India) and even abusive (as with the US). The country is threatened with an immediate exit – a leap into the unknown, which would exacerbate the already malicious blame game in British politics and between Britain and the EU.

The fiscal risks are also serious. Parliament could try to prevent an exit without an agreement. A result could be a general choice. If Mr. Johnson made this a vote on a no-deal Brexit and offered Mr Farage something juicy, he could get almost the entire Brexit vote while the Remain poll is split. That could give him a landslide. With the irresponsible promises he made in his leadership campaign, he could not do anything. British Chancellor Philip Hammond suggests that no deal would cost the Treasury £ 90 billion a year. Mr. Johnson's tax cuts could cost another £ 20 billion. There are also ambitious spending plans.

There are also constitutional threats. Mr Johnson has threatened to extend Parliament (the end of the parliamentary session) to prevent a deal from being negotiated. This would be an executive coup against Parliament. John Major, former Prime Minister, faces a judicial review. That would lead to a constitutional crisis – a result of injection of the foreign body of a referendum into a parliamentary system.

A bigger topic will be the future of the UK. Brexit is an English-nationalist project. All four nations of the Union could eventually go their own way. Scotland is the most obvious potential defector. Of course, independence would be more costly for Scotland if England were outside the EU. But in such situations people do not necessarily have to vote rationally – think of the English shouting for a dispute-free Brexit. The Northern Irish could also decide that they should better move inside to Ireland and into the EU, although the shock would be considerable for both parts of the island. Even Wales could eventually suffocate the embrace of "little England". Even without a collapse of the Union, the dispute between the four nations about the powers conferred by the EU will certainly be fierce.

I'm assuming that Brexit – probably a no-deal Brexit – is now inevitable. Another reason is the horror that many Europeans now feel. The fact that Mr. Johnson recently described the French as "shit" in a BBC interview (later cut out) is characteristic. This is how the Brexit party members of the European Parliament turned away from Beethoven ode to Joy was played. Why should Europeans tolerate such people if they have the choice?

The British have played an oversized role in the world. But how could the future of England be in open dialogue with the EU? One possibility would be to follow President Donald Trump's unilateralist and solipsistic US, probably as another enemy of the EU. The Corbyn option would probably be to support every supposedly leftist tyrant he can find. Can a country that wavers between Ayn Rand and Leon Trotsky really belong to the world? What justification can be given for his remaining as a permanent member of the UN Security Council?

What happens is not worthy of a serious country. The conclusion is that Britain is no longer such a country.

martin.wolf@ft.com