On the last day of a farewell European tour, Bush will press on with efforts to build European support for new sanctions if Iran remains defiant despite a carrot-and-stick campaign to get the Islamic Republic to suspend uranium enrichment.
Bush and Brown are expected to tread a more cautious line over the Iraq war, unpopular in both their countries and a source of deep anti-Bush sentiment in Britain.
Thousands of protesters demonstrated in central London on Sunday against Bush and the five-year-old war. Several demonstrators were injured in scuffles with police and authorities said they arrested 25 people.
Police in riot gear created a buffer to allow Bush's motorcade to reach Brown's Downing Street residence for dinner.
In a newspaper interview published on Sunday, Bush urged Britain - Washington's main ally over Iraq - not to withdraw troops unless conditions on the ground allowed.
"Our answer is: there should be no definitive timetable (for a pullout)," Bush told the Observer, adding he was "appreciative" that Brown was in frequent touch about "what he and his military are thinking".
The newspaper described Bush's comments as a warning to Brown, but the White House dismissed that tone, saying there was no disagreement between the United States and Britain on Iraq.
Only about 4,200 British troops remain in Iraq, most of them stationed at a base in the south. Britain has suggested it could pull them all out by the end of 2008, but with the situation still unstable in Iraq that appears difficult.
