Gordon Brown will resist the temptation to try to make some of the "Obama effect" rub off on him when he meets the US presidential candidate in London tomorrow.

Some allies hoped that the Prime Minister would break with protocol by holding a joint news conference with Barack Obama after their scheduled 45 minutes of talks in Downing Street. Instead, the two men will be pictured together but Mr Obama will be alone when he speaks to journalists afterwards.

Diplomatic niceties mean that Mr Obama must get exactly the same treatment as his Republican rival, John McCain, enjoyed when he visited No 10 in March. Officials said that getting too close to the Democrat candidate could backfire if the Republican candidate won November's presidential election.

Some Brown advisers feared that David Cameron might try to upstage the Prime Minister by speaking alongside Mr Obama or going on a brief walkabout with him after he leaves Downing Street, but that now looks unlikely to happen.

Mr Obama's talks with Mr Brown will focus on Iraq and Afghanistan, where they have a common agenda. Obama and Brown aides will swap notes on the Democrats' new-wave campaign techniques and Labour's public service reforms. Mr Obama will also meet Tony Blair in his capacity as Middle East envoy.