This Thursday’s United Kingdom general election is shaping up to be one of the closest fought British elections in modern times. According to the latest opinion polls, the Conservative Party, led by Prime Minister David Cameron, is virtually neck and neck with the socialist Labour Party, headed by Ed Miliband.

At present, no single party is projected to win an outright majority in the 650-seat House of Commons (326 seats are required for a majority), which makes another coalition government highly likely. Britain is currently ruled by a Conservative-Liberal Democrat coalition, which has been in office since May 2010.

One possible outcome of the election is a Labour coalition with the extreme left-wing Scottish National Party, which is expected to make sweeping gains across Scotland. The likely presence of more than 50 Scottish National Party members of Parliament in Westminster, with the possibility of several serving in a coalition cabinet, would have significant implications on British policy, some of which would be felt by the United States, especially in the realm of defense policy.

Here are five areas where this week’s British general election may impact the United States, depending on the outcome.

1. The Special Relationship

The Anglo-American alliance has been at the heart of U.S. and British foreign policy since World War II. Britain remains America’s most important ally on the world stage, with deep-seated military, intelligence, diplomatic, economic and cultural ties.

Britain’s Conservative-led government has made the partnership with the United States a top priority, and in his party’s manifesto, Cameron has pledged to “uphold our special relationship with the USA and further strengthen our ties with our close Commonwealth allies, Australia, Canada and New Zealand.” In contrast, none of the other British parties mention the special relationship in their manifestos.

If Labour comes to power, expect a greater public emphasis from Downing Street on the European Union, the United Nations and multilateral institutions, and less talk, at least initially, of a “special relationship” with the United States.

Miliband is also an inexperienced, unknown quantity on the international stage, and his relationship with the U.S. president will take time to develop. In practice, though, all British post-war governments have ultimately embraced the alliance with Washington as a necessity, exemplified most recently by Labour leader Tony Blair’s decision to stand shoulder to shoulder with George W. Bush in the aftermath of the 9/11 terrorist attacks.

2. National Security and Defense Policy

National security and defense policy have barely featured in the U.K. general election campaign, which has been dominated by domestic issues, including the economy, immigration and health care.

On foreign policy, there is little to distinguish between the two biggest parties on major issues such as the Iranian nuclear negotiations or Russia’s invasion of Ukraine. Cameron has, however, been more forthright than his Labour opponent on the global and ideological threat posed by Islamist terrorism, and has been more assertive in calling for British military intervention against ISIS.

The United States has been critical of defense cuts implemented by the present coalition government, but there is no sign of these cuts being reversed by the next British administration. With the exception of the United Kingdom Independence Party, none of the major British parties has pledged to spend the minimum required 2 percent of GDP on defense agreed to by all NATO member states.

Both the Conservatives and Labour are committed to renewing Britain’s independent submarine-based Trident nuclear deterrent, but the Scottish Nationals are in favor of a nuclear-free Britain. If the Scottish National Party enters a Labour-led coalition, the future of Britain’s nuclear deterrent will be called into question, weakening Britain’s position as America’s most valued NATO ally. Significantly, the U.K.’s entire nuclear deterrent is currently based in Scotland.

3. Britain’s Future in Europe

Britain’s future in Europe has been one of the biggest dividing issues between the Conservative and Labour parties. The Conservatives have promised to hold a referendum on Britain’s membership of the European Union in 2017 if returned to power, following a renegotiation of Britain’s relationship with Brussels.

The Labour Party has not supported a referendum, and a popular vote is unlikely to be held if Miliband becomes prime minister. While the Obama administration has aggressively called on Britain not to leave the European Union, and is more closely aligned with Miliband’s overall approach towards Europe, a British exit from the EU (or Brexit) would in fact strengthen the Anglo-American special relationship in the long run, and pave the way for a powerful U.S.-U.K. free trade area.

4. Economic Impact

After the economic decline of the Gordon Brown years, and over a decade of big spending Labour government policies which left Britain heavily in debt, the British economy began to stage an impressive recovery under the helm of Conservative Chancellor George Osborne. In 2014 the U.K. economy grew by 2.6 percent—its fastest rate since 2007. The rate of economic growth has, however, slowed considerably in the first quarter of 2015, and the U.K.’s national debt still amounts to £1.48 trillion.

If re-elected, the Conservatives are expected to continue to implement cost-cutting measures aimed at reducing government spending and reining in the debt. In contrast, a Labour government would be committed to increasing government spending, raising taxes and actively intervening in the economy. Such policies have prompted a warning by over 100 British business leaders that Labour policies would “threaten jobs and deter investment” in the U.K.

Britain’s economic recovery is important for Europe and for the United States. As the Congressional Research Service points out, “the U.S.-U.K. bilateral investment relationship is the largest in the world,” with roughly a quarter of total U.S. corporate assets abroad based in the U.K.—$5.1 trillion, as of 2012. A socialist victory in Britain could derail five years of austerity measures that have helped restore Britain’s position as the world’s fifth largest economy, ahead of France and Italy.

5. Scottish Devolution

If the Scottish National Party is brought into a Labour-led coalition government, the issue of Scottish independence will once again be brought to the fore of the British political debate, just months after Scottish voters emphatically rejected independence in a referendum last September by a margin of 55.3 percent to 44.7 percent.

A renewed call for Scotland to break away from the rest of the U.K. will fray nerves not only in London but in Washington as well, where there is concern that a resurgence of Scottish nationalism will threaten the future of the United Kingdom, undercut the special relationship, and question Britain’s nuclear deterrent.

This piece has been modified.