As Britain approaches a general election, likely to be held in March, every major poll points to a Conservative victory. The odds of Gordon Brown retaining the keys to 10 Downing Street look slim, and few would wager against the Tories. If he becomes prime minister, Conservative leader David Cameron will have an important opportunity to transform and rejuvenate British leadership on the world stage. As the world's fourth biggest military player, and sixth largest economy, the United Kingdom may not be a superpower, but remains a world power.

There can be little doubt that the domestic agenda will be the main focus for a Conservative government facing a stagnant economy, rising unemployment and a spiraling budget deficit. Mr. Cameron should not, however, back down from advancing British leadership on the world stage. He will have a strong team at his disposal, with William Hague and Liam Fox likely to retain their current foreign and defence portfolios.

After nearly three years of lackluster helmsmanship from Gordon Brown, a Conservative government must once again project a powerful British presence internationally. At the same time, Barack Obama's failure to assert robust U.S. leadership offers the Conservative leader a major opportunity to flex British muscle. The next U.K. government should not be afraid to aggressively assert a British footprint, both in Europe and across the globe.

A conservative foreign policy should rest on four key principles: the preservation of the Anglo-American Special Relationship and the trans-Atlantic alliance, the defense of British national sovereignty, the firm projection of military power in the defence of the national interest, and the advancement of freedom and liberty. All four principles must be underwritten by a strong military, which would mean a significant increase in defence spending above its current, historically low level of just 2.2% of GDP.

The heart of a conservative foreign policy must be the Special Relationship, the most important and successful partnership of modern times. It is the beating heart of the free world and the engine that drives the global war against Islamist terrorism. Under Messrs. Obama and Brown, the Anglo-American alliance has been weakened, through a combination of Washington's indifference and a series of strategic errors by London, including implicit support for the appalling release of Libyan Lockerbie bomber Abdelbaset Ali al-Megrahi by Scottish authorities. Disappointingly, the U.S. president has never mentioned Britain in a single major policy speech.

The next prime minister must make the full restoration of the alliance with the U.S. a top priority. He must also ensure that Britain's freedom to stand shoulder to shoulder with America is not constrained by the Treaty of Lisbon and the relentless drive toward ever-closer union in Europe.

The rise of a European Union superstate, with a Common Foreign and Security Policy and European Security and Defence Policy, directly threatens both British and American interests. The message should be sent loud and clear to the Obama administration that its strong support for a federal Europe is misplaced, and that a Conservative government will fight against any efforts by Brussels to take further powers away from London.

Under the Conservatives, Britain must be prepared to wield military might independent of the EU, and with the appropriate level of defence spending to back it up. On his recent visit to Afghanistan, Mr. Cameron showed a strong commitment to the 10,000-strong British mission, firmly rejecting the notion of a timetable for the withdrawal of NATO troops. He must also be prepared to use force, if necessary and as a last resort, alongside the U.S. to halt the rise of a nuclear-armed Iran, in addition to pressing for the European Union and the United Nations to impose a tougher range of political, economic and military sanctions against Tehran.

Finally, a Conservative government should pursue a foreign policy that places support for freedom on the world stage at its core. That includes supporting the aspirations of opposition movements in tyrannies such as Iran, Burma> and Zimbabwe, and standing up to dictatorial regimes that suppress their own people, and in many instances also act as state sponsors of terrorism.

Mr. Cameron should avoid embarking down the same engagement path traveled by Mr. Obama, which has succeeded only in emboldening America's enemies and weakening U.S. strategic power. He should forthrightly defend political dissidents who are fighting for freedom, from Moscow to Harare to Tehran, and studiously eschew the appeasement of tyrants. A Conservative administration must also advance a free trade agenda that supports the growth of economic liberty around the world, and confronts protectionist policies on both sides of the Atlantic.

Though largely untested in the foreign policy arena, Mr. Cameron undoubtedly has the potential to be an international statesman of significant stature. In order to achieve this he must be prepared to advance an agenda that projects strength, not weakness, and allocates the military resources required for Britain to operate successfully as a world power. The world needs strong British leadership, especially at a time when Washington is hesitating to take a stand on several fronts. Britain has a vital role to play in blocking the rise of a nuclear Iran, as well as winning the war in Afghanistan. A Conservative government should buttress Britain's alliances with the U.S. and NATO, while enhancing strategic partnerships with rising friendly powers such as India.

Under Mr. Brown, Great Britain is currently punching well below its weight as an international actor (except in Afghanistan). That must change for a nation with a proud history of global leadership, and a rich heritage that spans much of the world. Mr. Cameron should look not to Mr. Obama as a role model, but instead to Winston Churchill and Margaret Thatcher--two decisive and iron-willed leaders who took great pride in their country's past, while unashamedly advancing the national interest.

Nile Gardiner is Director of the Margaret Thatcher Centre for Freedom at the Heritage Foundation in Washington, DC.