Barack Obama downplayed the political implications of his weeklong trip to Europe and the Middle East Saturday, saying he wouldn't be surprised if he saw a downtick in his poll numbers upon his return.

The Illinois senator spoke to reporters in London on the final stop of his tour, after meeting with British Prime Minister Gordon Brown.

After a week of photo ops, high-level talks with foreign leaders and media coverage befitting an international celeb, Obama said he doesn't even know if the trip will help him -- in the U.S., anyway.

"You know, I'm not sure that there is going to be some immediate political impact. You know, I wouldn't even be surprised if that in some polls that you saw a little bit of a dip as a consequence," Obama said.

People in the U.S., he said, are worried about gas prices and home foreclosures.

"The reason that I thought this trip was important is that I am convinced that many issues that we face at home are not going to be solved as effectively unless we have strong partners abroad," he said. "And unless we get a handle on Iraq and Afghanistan, not only are we going to be less safe, but it's also going to be a huge drain on resources."

Rival John McCain's campaign teased Obama from afar over the past week, accusing him of making a premature victory lap. Polls taken during the trip showed negligible changes in public attitudes toward the candidates.

But Obama noted Saturday that McCain took a similar trip during the campaign season and also recently visited Latin America.

"He was telling me I was supposed to take this trip," Obama said. "Although I've got to admit we had it planned before he made the suggestion."

Since arriving in Europe, Obama has emphasized strengthening trans-Atlantic relations, first in a high-profile speech in Berlin and Friday during a meeting with French President Nicolas Sarkozy.

Obama said he and Brown discussed a wide range of issues, such as climate change, terrorism and financial markets.

"The prime minister's emphasis -- like mine -- is on how we can strengthen the trans-Atlantic relationship to solve problems that can't be solved by any single country individually," he said.

He said, "I think there is a deep and abiding affection for the British people in America, and a fascination with all things British that is not going to go away any time soon."

The Democratic hopeful seemed relaxed as he strolled down to the prime minister's office at 10 Downing St., pausing briefly to shake the hands of two somewhat startled police officers standing near the door.

He turned to television cameras, smiled, waved and said "hello" before walking into Number 10. Brown greeted him just inside the door.

Pooled television images showed Brown offering Obama a chair on the Downing Street terrace before the pair settled down for two hours of talks.

They later took a stroll in the sunshine around Horse Guards Parade, the vast open space where military reviews, such as Trooping the Color, are often held. Tourists snapped pictures from a distance while security guards walked ahead of the two men.

The walk offered a photo opportunity with a London backdrop for Obama, whose visit to Britain has been decidedly low-key, particularly after the huge crowds he drew earlier in the week in Germany.

Obama later said he had also wanted to take a walk through St. James' Park, but security guards pulled him and Brown back. The park is near Buckingham Palace, home of Queen Elizabeth II.

Obama stressed the importance of the bond between the two nations.

"We've been through two world wars together. We speak a common language. We share a belief in rule of law and due process," he said "We just like the people. There is a deep and abiding affection for the British people in America and a fascination with all things British that's not going to go away any time soon."

The Illinois senator also offered reassurance to Brown, whose plummeting popularity took another hit this week when he lost a parliamentary by-election in a Scottish seat long held by the governing Labour Party. But Obama pointedly said Brown didn't need his political advice.

"You're always more popular before you're actually in charge," Obama said. "Once you're responsible, then you're going to make some people unhappy."

From 10 Downing Street, Obama traveled a short distance to meet with David Cameron, leader of the opposition party. The two men sat in comfortable chairs in an alcove for their discussions.

Earlier, he met with former Prime Minister Tony Blair, who is now a Middle East envoy. The meeting lasted for just over an hour.

The Associated Press contributed to this report.