The two leaders have very different ideas about Britain’s role and place in the world.

As the post-Cold War foreign policy consensus around liberal multilateralism frays in the UK, the differences between the Conservatives and Labour are clearer than ever.

In Boris Johnson and Jeremy Corbyn, Britain has two contrasting characters who may become prime minister, each with very different ideas about the country’s place in the world, from its allies and partners to security and defence, to their understanding of the country’s historical role.

Corbyn seeks to reboot Britain’s foreign policy, making it more ethically driven and focused on questions of global justice. Johnson represents, beyond Brexit at least, a more conventional Conservative interpretation of British interests, though his focus on an independent trade policy implies a more mercantilist approach to international affairs.

The Brexit context makes these political differences on foreign policy matter all the more. Leaving the EU disrupts Britain’s relations with the continent, its biggest trade partner, and unpicks a security relationship which plays an important role in addressing modern threats, from terrorism to human trafficking. It will stretch the political ties with some of the UK’s closest allies and affect the country’s international reputation. And it may return to the UK powers currently exercised collectively, including the power to set an independent trade policy, with the attendant trade-offs this entails.

Beyond the politics of Brexit itself, how would the two leaders, Boris Johnson and Jeremy Corbyn, approach some of the most important international issues they would face as prime minister?

Relations with the US

Corbyn has been an outspoken critic of US President Donald Trump, contrasting with Johnson’s relative bonhomie with him. A major difference between the two is their approach to the prospect of a UK-US free trade agreement. Corbyn has made opposition to a future deal with Trump a major point in his campaign.

Other flashpoints under a Labour government could include the issue of Diego Garcia, the largest of the Chagos Islands in the British Indian Ocean Territory, which is home to a US military base. Labour has pledged to comply with an International Court of Justice ruling and allow the people of the Chagos Islands and their descendants to return to the islands from which they were removed (with the fate of the base unclear).

There would be very marked differences of policy with the US on the Middle East peace process, climate change and Iran, although on these issues the Conservatives are also out of step with the current US administration.

Victory for a Democrat in the US 2020 election, particularly a less conventional candidate like Bernie Sanders or Elizabeth Warren, alongside a Labour government in the UK, could create the potential for a uniquely progressive transatlantic partnership. Conversely, a Conservative government might find it has notably less in common with such a Democratic administration.

International security

Despite their very different politics, Trump and Corbyn do share similar assessments of the failures of recent US-led military interventions and have both been critics of NATO in the past – albeit from rather different perspectives.

Labour’s manifesto promises to end an approach it describes as “bomb first, talk later”. Corbyn has consistently opposed UK military action, from Kosovo and Afghanistan to Iraq, Libya and Syria. It is difficult to imagine the circumstances that would lead to a Corbyn-led government engaging in military intervention overseas, particularly if this were a US-led one.

Many voters in the UK will welcome a policy of greater restraint, given how some of these conflicts have played out. Others will fear the consequences of inaction in the face of states willing to commit atrocities or break international law.

Regardless, it would mark a significant shift in the UK’s defence posture, even if the Labour party remains committed to NATO membership and spending 2 percent of GDP on defence.

The Middle East

In the Middle East, a Labour government could lead to a sharp shift in direction in several areas. Beyond recognising Palestine, under Labour the UK could become a more vocal critic of the Israeli government, including at the UN, which in turn could potentially strain relations with the US under a second Trump term.

UK-Israel ties may also be further tested by the criticism of Corbyn’s handling of anti-Semitism within the party. This stands in contrast to recent Conservative government initiatives to deepen trade links with Israel, despite Israeli government actions in Gaza and the West Bank running counter to long-standing UK positions.

Under Labour, commercial defence ties that are an important aspect of the UK’s relations with the Gulf would face greater scrutiny. A Labour government would stop all sales to Saudi Arabia for use in Yemen and review Britain’s arms export regime. Meanwhile, Conservatives have defended these rules and continued to champion ties with Gulf countries, despite the fact that a British court has put a ban on new exports over human rights violations by the Saudi-led coalition in Yemen.

Both parties support the nuclear deal with Iran, although Johnson has been more sympathetic to the US position. Corbyn has sought to portray Johnson’s closeness to Trump as putting the UK at risk of being “dragged into a further conflict”.

China

On China, Labour and the Conservatives could strike a different balance between economic interests, security challenges and human rights concerns.

A Labour government would emphasise human rights, Hong Kong and concerns over the situation in Xinjiang, very possibly leading to a diplomatic cooling with China. Conversely, it may be less willing to risk provoking China by challenging threats to freedom of navigation in the South China Sea.

In contrast, a Conservative government would likely be more cautious in criticising China, certainly in public, with greater attention paid to investment and trade, although pressure from the US on issues like Huawei may yet move a Conservative government towards a more hawkish position.

Overall, where once there was a broad consensus, there are now significant disagreements in outlook and policy between the main parties. In this election, UK voters face a choice between two radically different visions of foreign policy.

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial stance.