US President George W. Bush and British Prime Minister Gordon Brown are confronting the twin challenges of Iran's nuclear ambitions and troop levels in Iraq in two days of talks capping the president's farewell tour of Europe. Their meetings amount to another get-to-know-you session between two leaders confronting their own woes at home. Bush, who remains widely unpopular in Britain, as he is in the United States, is pushing a broad trans-Atlantic agenda even as his influence wanes in his final months in office. And Brown's public approval has been undermined by rising food and fuel prices, unpopular tax changes and other troubles. The two leaders will discuss what progress is needed in Iraq before more US and British forces can return home, and both want to build international pressure on Iran to halt any possible nuclear weapons program, Bush's national security adviser Stephen Hadley said. Bush began his day with a bike ride and a church service in Paris, then shifted to London as his weeklong European trip neared its end. Security was tight in London as anti-Bush demonstrators prepared to vent their anger at the US president.