On Radio 4 on Monday Irwin Stelzer defined neo-conservatism. On the domestic front, it supports a free market, but acknowledges a role for the welfare state. It is socially liberal. Blair, then, is a neocon at home.

The controversial part, though, is the role it envisages for a government on the world stage. The argument goes that democracies don't fight one another, and that if powerful nations can increase the number of democratic regimes in the world, then they should.

Up until 9/11 Blair's principal criticism of US foreign policy was that it wasn't engaged enough. When Bill Clinton prevaricated over ground troops for Kosovo in 1999, Blair complained: "Americans are too ready to see no need to get involved in affairs of the rest of the world."

George Bush did not share the neocon agenda when he took office. He proclaimed on the campaign trail that under him "America doesn't do nation-building". Since 9/11 it has been a different story. In his first major post-9/11 speech, at West Point in 2002, Bush declared: "Our nation's cause has always been larger than our nation's defence."

In almost identical terms to Bush's West Point speech, Blair was speaking of Britain's gift of values to the world, back in 1997 in his speech at the Lord Mayor's Banquet: "In the end I am, simply, a patriot. I believe in Britain ... because, at its best, it does stand for the right values and can give something to the world."

It is the emphasis on "values" that links him to the neocons. Blair's formulation that, since the cold war, "our actions are guided by ... mutual self-interest and moral purpose in defending the values we cherish. In the end values and interests merge" is one that would be strongly supported by the neocons.

The distinction between values and interests is crucial. Interests are usually defended, values are promoted. Interests are material and can be defined, values are hard to pin down and know no limit. If we take the government's oft repeated mantra that "the best defence of our security lies in the spread of our values", British foreign policy at once becomes diffuse: our priorities are everywhere and nowhere.

What are these values? It is hard to disagree with Blair when he says: "Nations that are free, democratic and benefiting from economic progress tend to be stable and solid partners in the advance of humankind." The problem occurs when British security is linked to the spread of those values, and when we wage war in their name. British national interest is explicitly located in the internal affairs of other countries, violating international traditions of non-interference, and destabilising governments. No wonder countries in the Middle East are nervous.

I was studying in Chicago in 1999 when Blair argued for a "doctrine of the international community" legitimising humanitarian intervention in certain circumstances. The speech was well-received by leftwing fans of humanitarian intervention. But it was also seen as a seminal text by the rightwing interventionists at the University of Chicago and by neocons today.

The speech contained five tests for intervention. Are we sure of the case? Have we exhausted all diplomatic options? Is the military option practical? Are we in it for the long term? Are national interests involved? It was seen at the time as a defence of humanitarian intervention against the background of Kosovo. But when even the second war on Iraq can be justified retrospectively as "humanitarian", it looks more like an argument for using force to make the world a "better place", wherever politically and financially possible.

Where Blair departs from liberal interventionists and joins the neocons is the scope of his ambition. Humanitarian interest in military action stops at the achievement of the goal in question, whether stopping genocide in Serbia or removing Saddam. Blair's agenda is broader, almost imperial in scope. It is about using force to set examples.

Speaking of Kosovo in the Chicago speech, he said: "One of the reasons why it is now so important to win the conflict is to ensure that others do not make the same mistake in future ... we have to establish a new framework." This is the neocon philosophy in its purest form: war as the ultimate lever of change. The purpose of the war was to use force to establish the supremacy of our values. The same can be said of the war in Iraq. As one former US ambassador told me: "The reason for the war in Iraq was to have a war." And the prime minister seems to agree.

In Blair's words, what began as a unilateral war to enforce UN resolutions and disarm Saddam of WMD has been quietly transformed into "the battle of seminal importance for the early 21st century". According to Blair it is so important because this conflict "will define relations between the Muslim world and the west".

Blair says that the terrorists in Iraq agree with him about the importance of the battle. A coalition victory would mean "the death of the poisonous propaganda monster about America ... Lose the battle in Iraq and they lose the ability to present the Muslim world as victims and they as their champions". If losing would mean giving the terrorists the upper hand in the battle for hearts and minds in the Muslim world, then this war really was, as the US National Security Strategy puts it, a clash "inside a civilisation: a battle for the future of the Muslim world".

The neo-conservative thesis was always that the war on Iraq was part of the war on terror, that Afghanistan was not enough of a shock to shatter the confidence of states that would disobey the west. If we believe Blair's speeches after the war, paradigm change was part of the plan all along. To be clear, that means using military action as an instrument of foreign policy, not as a last resort.

The slide into "values" as the determinant of foreign policy unequivocally allies the UK to the US. The prime minister said in 2002 that the price for US engagement in the world is that "we don't shirk our responsibility. It means that when America is fighting for those values, then, however tough, we fight with her".

On this reading of UK policy, Blair would have sent troops into Vietnam. And based on this policy, the decision on whether or not the UK would wage war against Syria or Iran rests with the White House.

Depending on your point of view, this may or may not be a good thing for the UK. But in the words of Blair himself: "In the end, believe your political leaders or not, as you will. But do so at least having understood their minds."

Blair is the original neocon.

· Ben Rawlence was foreign policy adviser to the Liberal Democrats 2002-2004. He is currently writing a book on Tony Blair's foreign policy