British politics are in a state of upheaval as aftershocks of the U.K.’s explosive decision to leave the European Union continue to register. Negotiations seem to be in impasse and public opinion, particularly among the Brexiteers, is increasingly strident and resentful. Why don’t we just leave? Why the prevarication? Why can’t we simply “take back control”?

The very fact that such questions are asked – and they are asked frequently and noisily – is testimony to then–Prime Minister David Cameron’s huge miscalculation in calling the 2016 Brexit referendum. The decision to hold a referendum on a matter of such bewildering complexity and with most voters so poorly informed doubtless will be regarded as one of the most debilitating political mistakes in modern British history. The key issues now being discussed are the U.K.’s relationship to the EU’s customs union and its single market, and the problem of the Northern Ireland border. None of these were discussed during the referendum campaign.

There is a major underlying political problem which threatens to scupper any chance of a sensible and acceptable deal. For over half a century the issue of U.K. membership in the European Union (formerly the European Economic Community, or EEC) has disrupted the British party system. The principle of membership has time and again fractured both the Conservative and Labour parties. In fact, the reason why the constitutionally highly anomalous (in the British context) device of the referendum was first introduced, in 1975, was to manage internal party differences.

In 1973, it was only through the support of 60-odd Labour MPs that the Conservative government of Edward Heath obtained a Commons majority in the decisive vote to join the EEC. Many in the Labour Party were furious and insisted on a pledge for Britain to leave the EEC. Others, equally firmly, wanted to stay. With the party evenly divided, its leader, the astute and wily Harold Wilson, seized on the stratagem of a referendum (first floated by current Labour leader Jeremy Corbyn’s mentor, Tony Benn) as a way of keeping the party together. He promised to renegotiate the terms of entry and then hold a referendum, a course he followed when Labour returned to power in 1974. The “renegotiation” was mainly fictional, but Wilson recommended acceptance, and although Labour was split down the middle the country voted by a two-thirds majority in favour of staying in the EEC.

Labour’s “antimarketeers” were mainly left-wingers, and when Margaret Thatcher’s victory in 1979 drove Labour into opposition the party swung sharply to the left. Its 1983 election manifesto contained a promise to withdraw from the EEC. Labour was crushed in the election and the left was marginalized. What then occurred was a strange case of political role reversal. Thatcher adopted an increasingly belligerent and nationalistic posture. This helped precipitate her ejection from office, and it had the longer-term effect of giving a major impetus to anti-EU sentiment among Conservatives. This, combined with the challenge of the rapidly-growing anti-EU United Kingdom Independence Party (UKIP), persuaded Cameron – in a repetition of Harold Wilson’s stratagem 40 years earlier – to promise a referendum prior to the 2015 election, in order to maintain Conservative unity.

UKIP has sunk into irrelevance, but hostility toward the EU – now channelled into a clamour for a “hard Brexit,” even a “no-deal Brexit” – is stronger than ever in the Conservative Party. This was made plain by the tumultuous reception accorded to the hard-Brexit cheerleaders, former Foreign Secretary Boris Johnson and the rather bizarre darling of the Brexiteers, Jacob Rees-Mogg, often described as the MP for the 18th century.

At present, the Conservatives are divided between support for the so-called “Chequers deal” and the so-called free trade “Canada plus” approach – named after the laboriously negotiated free trade deal between Canada and the EU. Complicating the issue is the struggle for the Tory succession. Prime Minister Theresa May is stubborn and diligent but rigid and robotic in style and manner. She forfeited the support of much of her party with its unexpectedly poor performance at the 2017 election, in which the Tories preserved a narrow majority in Parliament only by forming an alliance with a small party representing Northern Ireland Protestants. Rivals sense she cannot long survive, and Johnson, Rees-Mogg and several senior minsters are snapping at her heels.

What of Labour? After 1983, its anti-EU stance was ditched and party policy moved toward a position of constructive (although never entirely full-hearted) engagement with Europe. This remains the majority position. But the party has so far failed to formulate a coherent, realistic and convincing stance on Brexit. This is not surprising since the new leadership has had to balance and accommodate a range of pressures and preferences – political, ideological and electoral.

The first point to make is that divisions over the EU no longer coincide with Labour’s left-right cleavage. Both left and right within Labour are divided between Europhiles and Eurosceptics. The majority of the party’s right and centre are Europhiles; many are Remainers favouring a second referendum. But there are also a significant number of right-wingers who object to a second referendum, either because they are Eurosceptic (four of the five Labour MPs who recently voted with the government on the issue are from the right) or – the larger number – because they fear that any shilly-shallying over Brexit will tarnish Labour’s appeal to working-class Brexit voters in their constituencies.

The left, which now controls the leadership, is also split. Corbyn and some others – such as his key lieutenant, shadow chancellor of the exchequer John McDonell, and his highly influential adviser Seamus Milne – have long labelled the EU a “capitalist club.” Their views are essentially unchanged from the 1970s: they see the EU as embedded in free-market principles, institutionally averse to state intervention and public ownership, and solidly attached to a restrictive fiscal orthodoxy. All this will, it is argued, constrain Labour’s ability to pursue more radical policies.

Many of the younger rank-and-file Corbynistas dispute the above analysis as overstated and accuse Corbyn of ignoring the wider economic consequences of Brexit. This is a view also taken by most affiliated trade unions. For the unions, the issue is not simply one of economics; culture and values matter.

Here we must acknowledge the elephant in the room. Most Brexit voters knew little and cared less about the intricacies of trading relations, the EU’s consumer and environmental regulations or its regional policies. They cared very deeply and often viscerally about immigration. This was partly misgiving about alleged pressure on jobs, wage levels, housing location, health care and so forth. It was also about culture and identity, the threat to British (or English) customs, values and ways of living posed by mass immigration. It should be noted that most Brexit voters make no distinction between EU migrants, refugees and members of ethnic minorities arriving from Africa or South Asia.

Conversely, for many in Labour’s ranks, EU membership has become a touchstone of a wider social ethos defined by equality, tolerance, internationalism and openness, and of their repudiation of the narrow, particularistic ethnonationalism and anti-immigration sentiment voiced by many Brexiteers.

These political and ideological matters intersect with Labour’s electoral interests. Labour’s 2017 electorate divided two thirds / one third between Remainers and Leavers. Its major gains were among young, well-educated professionals living in the south, all categories that exhibited high support for staying in the EU. Conversely, there was a below-average swing to Labour, or none at all, among older, less-well-educated voters, the working class and voters living in the north and Midlands, all of whom favour Brexit. To further complicate Labour’s problems, although most Labour voters were Remainers, the majority of Labour MPs represent majority Leave constituencies.

The Labour leadership is well aware that to conciliate both Remainers and Leavers is a tricky balancing act. The leadership believes undue policy clarity will render conciliation even more difficult. Hence, it opts for a stance of “studied ambiguity.” This is an accurate description; it is not a policy. At Labour’s September policymaking conference, very large numbers of constituency parties submitted resolutions demanding a second referendum. Some clarification was required.

Responsibility for hammering out a compromise was assigned to Labour’s shadow Brexit secretary, the exceedingly able Keir Starmer. The resolution eventually formulated and overwhelmingly endorsed at the conference was vague but an improvement on “studied ambiguity.” The resolution stated that the party’s preferred way of tackling Brexit is a new general election to elect a Labour government; if an election is blocked, then a referendum would be “on the table.”

But a referendum on what? Earlier, senior Corbynistas had insisted that it must be confined to a vote on whatever deal the government agreed with the EU, and not be a rerun of the 2016 referendum. In his conference speech, however, Starmer stated in an unscripted comment that a second referendum could include a Remain option. The response of the conference audience, packed with left-wing delegates, was instructive: loud and prolonged cheering culminating in a standing ovation. There is no doubt where Labour’s heart lies. In stark contrast, in his leader’s speech Corbyn’s only reference to a second referendum was a scarcely audible mumble; it was as if a tooth had been unwillingly extracted.

So where does this leave Britain? In a word, in a mess, buffeted by the storm winds of an ever more volatile political climate. Neither a general election nor a referendum seems likely. The rules governing the calling of an election have changed. There will be a full five-year term unless two thirds of the Commons decides otherwise. A second referendum would need an act of Parliament – that is, approval by a majority of the Commons. The government has said it is adamantly opposed.

To break the logjam, May now appears to be putting out feelers to pro-EU (and anti-Corbyn) Labour MPs to help navigate through the Commons a package palatable both to her government and to the EU. With pressure already mounting among Labour activists to deselect anti-Corbyn MPs, this would be a hazardous step for centrist Labour MPs.

Not since the 1970s has the U.K. party system seemed so unstable. Both major parties are bitterly divided and rife with rumours about leadership challenges and the formation of a new centrist party. Aftershocks of the volcanic 2016 referendum eruption are still being felt.