Republican presidential candidate Rudy Giuliani met with Britain's prime minister Wednesday and vowed the U.S. would take any action necessary to keep Iran from becoming a nuclear power.

The former New York mayor is the latest GOP candidate to travel to Britain, meeting the new political guard and visiting former Prime Minister Margaret Thatcher, an icon for U.S. conservatives.

Giuliani met Prime Minister Gordon Brown and his predecessor Tony Blair. He was to deliver a lecture at the Atlantic Bridge, an organization that promotes ties between British and U.S. conservatives.

He said he discussed Iran with Brown and was "very, very much heartened by how seriously he sees it." He insisted Iran would not be allowed to become a nuclear power soon.

"We will use any options we believe is in our best interest to stop them becoming a nuclear power. With the absolute assurance that if they get to the point that they are going to become a nuclear power, we will prevent that or set them back five or 10 years. That is not said as a threat. That should be said as a promise," he said.

Giuliani's moderate stances on gun control, abortion and gay rights have put him at odds with many U.S. conservatives and religious leaders. But several world leaders have sought his opinions on security in the wake of the terrorist attacks on Sept. 11, 2001, when he was mayor of New York.

He said the alliance between the U.S. and Britain was essential to defeating terrorism.

"It is now such a strong relationship that it is going to endure whatever we have to endure to overcome Islamic terrorism," Giuliani said.

The trip to London also was an opportunity for Giuliani to raise money for his presidential bid. A $1,000 per person luncheon was planned at the Mandarin Oriental Hyde Park for U.S. citizens to give to Giuliani's campaign. The event featured a question-and-answer session between Giuliani and Winston Churchill's granddaughter, Celia Sandys.

Fred Thompson and Mitt Romney, two other Republican candidates, have also recently come to Britain to visit Thatcher — dubbed the "Iron Lady" by the Kremlin during the Cold War and considered a mentor to many conservatives who are trying to distance themselves from the policies of President Bush ahead of the elections.

Thatcher is remembered by many in the United States for her close relationship with former President Reagan, who died three years ago.

Giuliani said recently that the United States was lacking "strong, aggressive, bold leadership like we had with Ronald Reagan."