This week something unprecedented will happen in Britain. An American president will arrive here and be greeted not by cheering crowds but by howls of execration. The protests in London against George Bush are likely to be the biggest Britain has seen since the anti-war marches in February. The people of the United States will be deeply shocked to see how the image of their government has changed.

Those of us who oppose George Bush’s policies are often accused of being “anti-American”. It’s an odd charge. No one suggests that people who don’t like Tony Blair are “anti-British”. It seems to be an attempt to discredit us by suggesting that we are motivated not by reasonable political objections, but by an old and visceral contempt for an “upstart nation”.

But perhaps the gravest of the charges we can lay against George Bush is that he is himself an anti-American. His style of government stands at odds with everything we were led to believe the United States of America represents. There is first the question of his election. The evidence that the electoral roll in Florida was rigged in order to exclude black voters appears to be compelling. The conduct of his party both during and after that election appears to be a grotesque insult to the nation which invented modern, Jacksonian democracy.

Then there is his assault upon civil liberties. The Patriot Act he pushed through Congress erodes many of the freedoms the American constitution appears to guarantee. In the offshore prison camp of Guantanamo Bay, Bush appears to have built his own Bastille, in which people are jailed indefinitely without charge or trial. George Washington and Thomas Paine must be turning in their graves.

But the greatest of all his offences against American values is his construction of what looks very much like an imperial project. If the US stands for anything in the popular imagination it stands for national sovereignty and self-determination. It tore itself away from a grasping empire – our own – and declared its opposition to all subsequent attempts to bend sovereign peoples to the will of a distant nation. It came to the rescue of its old imperial oppressor when our own sovereignty was threatened by Hitler, and ever since then we have identified America as the champion of those nations which struggle against occupying powers. But now Bush has invaded and conquered a sovereign nation and installed in it a regime scarcely distinguishable from the old European colonial authorities.

To make this occupation possible, he and his staff appear to have misled us on several occasions. We were told that Iraq had to be invaded because it possessed weapons of mass destruction which threatened the lives of the people of other nations. We now know that the US government possessed plenty of intelligence showing that this was unlikely to be true. We were told that Saddam Hussein was establishing links with Al Qaeda. It now seems that there was no substantive evidence that this was taking place; indeed Al Qaeda appears to have begun entering Iraq only when Saddam was deposed.

We were told that Iraq had to be invaded because George Bush and Tony Blair could not bear to leave its people suffering under such a monstrous regime. But the same governments are now providing military and diplomatic assistance to the president of Uzbekistan, who boils his political opponents to death.

All this has become our problem, as well as that of the Americans and the Iraqis, because whenever George Bush says “jump”, Tony Blair asks “off which high building?” It appears that the White House can hatch no project which is doomed or crazy enough to prevent Blair from joining in. It is a constant source of mystery to me that British patriots expend so much energy in complaining about threats to our sovereignty from the European Union, yet somehow choose to overlook the graver threat presented by our subordination to Bush’s government. Blair has surrendered our foreign and defence policy to Washington. The defence secretary, Geoff Hoon, has even begun to restructure our armed forces to make them structurally and functionally subordinate to those of the US.

Next week, Tony Blair will be showing Bush around town much as an imperial prefect might have led the Roman emperor around a newly-acquired domain. We cannot depose this new emperor (it is even doubtful whether his own citizens can do so), but we can show him that his policies, and our government’s submission to them are unwelcome here.

It is sometimes easy to forget, in the midst of a furious crowd, that all our liberties were acquired not through polite representation, but by means of insurrection and protest – from the Boston tea party to the demonstrations of the suffragettes. When the governing powers lose sight of the people, protest is often the only means of reminding our leaders that we still exist. It is messy and troublesome, but it is often all we have.

Our purpose next week is to show the American people that even the people of the nation Bush regards as his closest political ally reject his policies. Nothing could be more damaging to a man whose credibility is already gravely challenged at home. Let us peacefully flood the streets of London on Thursday, not because we hate George Bush’s country, but because we love the values it is supposed to embody.

George Monbiot’s new book The Age of Consent: a manifesto for a new world order is published by Flamingo.