Private meeting inside Downing Street means PM can't bask in Obama glory

In what has been dubbed the "battle of the photo opportunities", both Tony Blair and David Cameron will enjoy high-profile meetings with the US Democratic Party's presidential candidate but Mr Brown will be forced to conduct his business with Mr Obama largely behind closed doors.

In the wake of Mr Obama's successful visit to Berlin yesterday - where he delivered a widely praised and statesmanlike speech in front of adoring crowds - the Prime Minister might have hoped to share some of the American's limelight to offset the Glasgow by-election defeat and the debate over his leadership.

But in contrast to the Berlin visit, Mr Obama's brief London stopover will be carried out in almost complete secrecy with no plans for joint press conferences and only tightly controlled photo opportunities.

When Mr Obama arrives in Downing Street for a breakfast meeting tomorrow-Mr Brown will be unable to appear on the steps at No10 with his guest, because he did not do the same for John McCain, the Republican Party's candidate, when he visited in May. Protocol therefore requires that Mr Obama and Mr Brown conclude their meeting and pose for the formal farewell handshake photographs behind the doors of No10, considered a much less flattering photographic-moment than appearing in front of the flashbulbs and TV cameras on the steps outside. Mr Obama will then address the waiting media alone.

The Downing Street talks will be sandwiched between an earlier meeting with the former prime minister - who has a much higher profile than MrBrown among Mr Obama's voters - and a later one with the Tory leader at the Houses of Parliament.

Mr Obama's discussions with MrBlair, appointed as a special Middle East envoy after leaving office, will focus on the Israeli-Palestinian peace process and on climate change.

According to some reports, Downing Street raised objections to initial plans for Mr Cameron to be photographed walking with Mr Obama towards Parliament - a photo opportunity both would have relished - and instead the Conservative leader will be pictured with his guest in New Palace Yard inside the Palace of Westminster, as he was with Mr McCain, therefore ensuring "protocol parity" is observed.

A tight security cordon will surround the US senator, with heightened protection from Scotland Yard, in what is believed to be an unprecedented move for a private visit.

The operation will be far more discreet than the measures taken during the visit of George Bush last month, when more than 2,000 police officers were deployed on the streets.

Mr Obama will instead be shadowed by US secret service agents and armed "close protection" officers from the Yard. One senior Met source said: "We are acutely aware of his status and the risks of assassination. There will be close protection."

Vehicle restrictions are likely to be in place temporarily in some streets in central London while a police helicopter will fly overhead.

Although Downing Street remained tight-lipped on details of the 18-hour visit, sources said Mr Obama was due arrive in a private jet at Heathrow at about 8pm from Paris.