PRESIDENT BUSH touched down at Heathrow last night inside an unprecedented ring of armour to begin one of the most controversial state visits to Britain for many years, with the most security and ceremony accorded to an American leader since Woodrow Wilson came to London in 1918.

Accompanied by his wife Laura, the President landed in Air Force One at 7.22pm on the far side of London’s main airport to receive a low-key welcome from the Prince of Wales. In keeping with the largest operation in memory to protect a visitor from the twin threats of demonstrations and terrorism the Bushes left at once in the presidential helicopter Marine One for the heavily guarded gardens of Buckingham Palace, where they are guests of the Queen.

They took an aerial detour via Tower Bridge and the illuminated landmarks of Central London, and flew directly over hundreds of protesters marching from the Strand to the American Embassy.

The visit is of major importance to Tony Blair, Mr Bush’s principal ally in the Iraq war, but with many thousands of demonstrators preparing to take to the streets to voice opposition to US and British policy in the Middle East, security chiefs on both sides of the Atlantic wish the trip could have been postponed to a more propitious time.

But Mr Bush will risk the wrath of his critics by insisting that he is committed to strong international institutions and alliances that are effective.

He has been criticised for a unilateral approach to war, arms control and climate change, but he will counter by saying that he is interested in multilateralism that produces results and in using the world’s institutions if they are prepared to face up to today’s global challenges.

He will also say that there may be times when he decides that he has to use force again. “He will say that we have to recognise that times will come when the use of force is necessary,” a senior administration official said.

In an address billed by aides as a major foreign policy speech, Mr Bush will confront European capitals sceptical of his call for a democratic Middle East. “He’ll challenge great democracies to recognise the importance of those values for security and for prosperity,” the official said.

His speech, at the Banqueting Hall in Whitehall, will address what he will call the three pillars of peace and security: strong institutions and effective alliances, a willingness to defend the peace with force, and the spread of democratic values around the world.

Mr Bush will point to his approach to North Korea and Iran as proof of his multilateralism. He will also cite his decision to take the issue of Iraq to the United Nations twice in search of support as evidence that he believes in institutions, as long as they are prepared to face up to issues.

Mr Bush’s approach risks a transatlantic culture clash between US views of the UN as a body that frequently fails to deliver, and the view of many Europeans that the UN should be respected at all costs.

At the same time officials ruled out any announcement during the three-day trip on whether the US will scrap steel tariffs, the issue dividing the Iraq war allies. Nor is any significant movement expected over the issue of British prisoners held at Guantanamo Bay.

Last-minute security fears have led to Mr Bush, whose Secret Service codename is Trailblazer, cancelling his only major public appearance during his three days in London. The President has hurriedly dropped plans to meet the families of the British victims of the September 11 attacks, at the memorial garden outside the US Embassy in Grosvenor Square this afternoon. This event would have been the longest time that Mr Bush was in public view and the closest that he would have got to wellwishers and demonstrators.

The official reason for the sudden change of heart is that Mr Bush wants this emotional meeting with the families to take place away from the public glare, so that their private talks will now be held inside the heavily fortified embassy. The President agreed to this change just before he boarded Air Force One to begin his journey.

Nervous Secret Service agents are reportedly worried that protesters in Grosvenor Square may have tried to emulate the veteran peace campaigner, Lindis Percy, 61, who eluded police and scaled the gates of Buckingham Palace.

This means that apart from his official welcome from the Queen in the forecourt of Buckingham Palace this morning, all the public will see of Mr Bush is him getting in and out of his armour-plated car after a 100-yard drive from the side of the Palace to the front.

The Secret Service fear that they are facing a triple threat.

Britain is now at its highest state of alert since the September 11 attacks after a terrorist suspect in custody told detectives of a 15 to 20-strong cell of Algerian supporters of al-Qaeda, who are ready to launch a terrorist attack.

Their intended targets are understood to be synagogues in London and Manchester. While this al-Qaeda threat is not specifically linked to Mr Bush’s visit, this terrorist cell may use the timing to stage an attack using suicide bombers to grab maximum publicity.

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