Passersby got a shock today when Gordon Brown and Democratic presidential candidate Barack Obama took a stroll through the park - complete with secret service agents in tow.

Mr Obama, who was in London meeting with UK political leaders  took a walk along Horse Guard's parade with the PM during a two-hour meeting.

During his visit, Mr Obama  thanked Britain for its role in Afghanistan and Iraq and promised a faster and better peace plan for the Middle East if he becomes President of the United States.

Gordon Brown and Democratic presidential candidate Barack Obama take a stroll along Horse Guards Parade - behind Number 10 Downing Street today

The two men continue to walk and talk as Mr Obama's secret service men keep an eye on things

The Democratic presidential candidate also offered some words of support to Prime Minister Gordon Brown.

'Everyone is always more popular before they take charge and once you become responsible you are going to make people unhappy - it's the nature of politics,' he told a media conference.

Fresh from a meeting with Tony Blair this morning, Obama met Mr Brown in a two-hour visit at Number 10 Downing Street where the pair spoke on a range of issues.

As well as the on-going situation in Iraq and Afghanistan, they also discussed climate change, international terrorism and global economics.

Mr Obama also pledged more troops for Afghanistan and outlined a 16-month timetable for the withdrawal of U.S troops in Iraq.

Passersby get a shock as the two high-profile men walk by

But the Prime Minister told the Commons on Tuesday that it would be next year at the earliest that the number of UK forces in Iraq could be significantly reduced from the current 4,100.

Mr Obama's meeting with the Prime Minister followed one with former PM Mr Blair earlier this morning to discuss developments in the Middle East peace process.

Arriving overnight from Paris, Mr Obama spent the night in at the Hyatt Regency Churchill hotel in central London with his 200-strong entourage ahead of his meeting with Mr Blair, who arrived at the hotel at 7.30 am.

Mr Blair left the hotel by a side entrance an hour later.

Mr Obama followed through the same exit six minutes later, waving before getting into a black Mercedes Viano.

Around a dozen passers-by took his photo on cameras and mobile phones as he left.

His car was followed by several other Mercedes vehicles and three minibuses carrying his staff and press before moving onto Downing Street for breakfast with the Prime Minister.

The PM and his visitor are all smiles in the garden of Number 10 Downing Street

Barack Obama waves to the waiting media from the steps of Number 10

He was driven into the street through the Foreign Office entrance as the main Whitehall entrance was closed for building work.

Mr Obama shook hands with one of the police officers on duty in the street before tuning and waving at the dozens of waiting TV cameras, photographers and journalists.

He smiled and said: 'Hello' before walking into Number 10, where he was greeted just inside the door by Mr Brown.

After the meeting, Democrat Mr Obama held a mini-press conference in Downing Street using the iconic image of the black No10 front door as a backdrop.

But strict protocol means Mr Brown did not appear alongside him because he did not do so with John McCain, the Republican rival for the presidency,  when he was in Britain in May.

Mr Obama rounds off his UK political tour with Tory leader David Cameron

Hopeful: Barack Obama meets with Mid-East envoy Tony Blair inside the Hyatt Regency Churchill hotel this morning

Instead the customary handshake and farewell photographs were  taken inside by the Downing Street fireplace.

White House hopeful Mr Obama then travelled the short distance to the Houses of Parliament by car for a brief meeting with David Cameron in the Conservative leader's office overlooking the Thames.

Mr Cameron pointed out a few of the historic building's features as they posed for photographs before going inside for talks.

Mr Cameron and Mr Obama spent almost an hour talking in the Tory leader's Commons office first with shadow foreign secretary William Hague and shadow chancellor George Osborne and then one-to-one.

The pair chatted about Mr Cameron's wife, Samantha, and their three children as well as his own holiday plans - a family break in Cornwall.

A Tory spokeswoman said the talks centred on the economy, with the two men agreed that 'short-term fixes would be no good unless in a long-term framework'.

Hello London: Barack Obama steps off his plane

Mr Obama has used his trip to call for the ties between Europe and America to be reinvigorated after damaging splits under George Bush's presidency over Iraq.

But his refusal to appear in public will disappoint many of his UK supporters - and the large American community in London.

Some Obama fans gathered at the gates of Downing Street in the hope of catching a glimpse of the Illinois Senator with star quality, which drew massive crowds in Berlin.

While in Berlin, Mr Obama made a keynote speech of the European-leg of his globetrotting tour, which has also taken in Jordan, Israel and the Palestinian territories.

'The burdens of global citizenship continue to bind us together,' he told them.

'If we're honest...we know that sometimes, on both sides of the Atlantic, we have drifted apart and forgotten our shared destiny.'

Mr Obama's London visit comes hours after meeting with  French President Nicolas Sarkozy in Paris.

Ahead of his arrival, Mr Sarkozy told Le Figaro newspaper that Obama was 'my pal'.

'Unlike my diplomatic advisers, I never believed in Hillary Clinton's chances. I always said that Obama would be nominated,' he added.

Obama's plane lands at Heathrow

Mr Obama used the meeting as an opportunity to call on France to contribute more troops to the Nato-led mission in Afghanistan before flying onto London last night.

Mr Obama's UK visit is in stark contrast to the astonishing scenes in Berlin where he was cheered by a 200,000-strong crowd.

The U.S presidential hopeful, who flew into Britain last night, kept his short visit relatively low key.

His London stop-off formed the final part of his flying global trip which is designed to boost his foreign policy credentials.

But Mr Obama's trip, which saw him visit seven countries and cover 10,000 miles, has been met with heavy criticism by McCain campaigners.

Speaking about Obama's popular support in Berlin Mr McCain said: 'I would love to give a speech in Germany - but I would rather give it as President of the United States.