Britain's participation in any U.S.-led war on Iraq may seem a foregone conclusion, especially now that the U.N. Security Council has unanimously accepted a new U.N. resolution designed to disarm Iraq once and for all -- one that Britain helped the United States write.

But before Prime Minister Tony Blair can lead Britain into war, he must slay two dragons in his path: dissent within his own government and party, and opposition among European Union countries to a war on Iraq.

Britain's support in this war would be considerable. Reports from London indicate that more than 30,000 British troops would join in a U.S.-led offensive. Britain would play a leading role in the international security force in a post-war Iraq as well: Up to 15,000 British troops are expected to remain for up to five years after Saddam Hussein has been deposed.

But for that to happen, Blair must show real leadership within the House of Commons and in Europe, where anti-American sentiment is heavily entrenched.

The Labor Party's Old Left considers Iraq "the new Vietnam." This group of unreconstructed socialists is united by a shared hostility to U.S. foreign policy and a visceral hatred of the Bush administration. Blair has begun reforming the Labor Party, but so far he has failed to dislodge the old unilateral disarmament coterie that discredited the party during the Cold War.

This group includes ministers such as Clare Short, the pro-Palestinian International Development Secretary who resigned from the Labor Shadow Cabinet in 1991 over the first Gulf War, and Robin Cook, leader of the House of Commons. Among the 160 backbench ministers who have signed a motion opposing military action against Iraq are George Galloway, who, in between trips to Baghdad, has described Britain as "the tail of the American dog," and Alice Mahon, whose said the Pentagon's advocacy of pre-emptive strikes meant "the lunatics have taken over the White House."

Such views, by no means unusual among the Labor rank and file, are undoubtedly an embarrassment to the prime minister, who has faced increasing anti-American sentiment within his own party over the United States' handling of the Arab-Israeli conflict and the International Criminal Court.

For Blair to play a full role as America's key partner in a war with Baghdad, and thus continue to maximize British international influence, he will need to face down his critics in the Labor Party, in what may prove to be the most important confrontation with the Labor left since he became prime minister in 1997. Blair shouldn't be afraid to sack dissenters in his cabinet, including Short and Cook. Indeed, Blair should use the Iraq debate as an opportunity to assert his authority and remove some "dead wood" in his party.

The prime minister also will need to confront America's critics in Europe, including German Chancellor Gerhard Schroeder, whose political opportunism and ostrich-like failing to confront the Iraqi regime should be condemned. The continuing appeasement of Iraq by the EU and Germany is one of the most short-sighted episodes of post-war European history.

The European Union, led by Commission President Romano Prodi and External Relations Commissioner Christopher Patten, will use opposition to an Iraq war to attempt to project its influence on the global stage, in a vain effort to portray itself as a major world player. Euro-federalists are outraged by the closeness of British foreign policy to that of America's. "Morally and politically, we could take charge in the world," says Belgian foreign minister Louis Michel. "But the British are blocking that. They still don't understand that they could play a pioneer role in Europe instead of submissively following the U.S."

Britain's position as a leading global player has been greatly enhanced since Sept. 11, in large part due to Blair's standing "shoulder to shoulder" with President Bush. As the primary nation in Europe able to project substantial military strength beyond the continent, Britain has emerged as the world's second most powerful military and political power in the 21st century. It is no coincidence that it was the only nation to join the United States in launching military strikes on the opening day of the Afghanistan offensive.

The closeness of the Anglo-American relationship undoubtedly causes envy and disquiet among a resentful Brussels establishment, who feel militarily inadequate and virtually irrelevant on the world stage. But, whether they like it or not, the Europeans have a choice: They can carp on the sidelines, or they can join Britain and the United States in an historic war to remove one of the most evil regimes in modern history.

Dr. Nile Gardiner is a visiting fellow in Anglo-American security policy and John C. Hulsman, Ph.D., is a research fellow in European affairs at The Heritage Foundation (www.heritage.org).