You hope, Sir, that I think the French deserving of liberty? I certainly do. I certainly think that all men who desire it, deserve it. It is not the reward of our merit or the acquisition of our industry. It is our inheritance. It is the birthright of our species . . . A positively vicious and abusive government ought to be changed and, if necessary, by violence, if it cannot be (as sometimes it is the case) reformed.

Edmund Burke

Freedom of expression, a free press, freedom of assembly and the right to demonstrate peacefully are basic rights - they are as much the rights of people in Tahrir Square as they are of people in Trafalgar Square. They are not British or western values, but the values of human beings everywhere.

David Cameron

It is well known that the Conservatives, like most other big political parties, have always been a coalition. This is true most obviously with regard to domestic issues, but every now and again the Tories divide bitterly on foreign policy as well. In the 1930s, they were at odds over the appeasement of Hitler, which Chamberlain's government supported and a minority under Winston Churchill, Harold Macmillan and Anthony Eden strongly opposed.

In the mid-1950s, a small number of Conservatives broke ranks with Eden over Suez. After the end of the cold war, during the 1990s, the question of "Europe" nearly tore the party apart. There was another split in 2003, when most Tories supported the decision to remove Saddam Hussein but a substantial group, Kenneth Clarke prominent among them, disagreed. Now the party is divided once more, this time over whether or not to intervene against the floundering regime of Colonel Gaddafi in Libya.

The closest parallel to current events is not appeasement, Suez, European integration or Iraq, but the Bosnian war of 1992-95. During that conflict, tens of thousands of Croatian and Bosnian civilians were murdered, while hundreds of thousands were displaced or made refugees. These developments were not the by-product of fighting but the pur­pose of a war being waged - as the Inter­national Criminal Tribunal for the former Yugoslavia later put it - in support of the "joint criminal project" to create an ethnically pure "Greater Serbia".

The European Union and then the UN proved powerless to stop the violence. Both organisations confined themselves to the despatch of humanitarian aid, plus a substantial peacekeeping force to safeguard its distribution. "Safe Areas" were established to protect the Muslim population, but these were attacked with impunity by the Serb militias, culminating in the Srebrenica massacre of 1995.

At that time, the Conservative government of John Major and most Westminster Tories were resolutely opposed to intervening militarily against the Bosnian Serbs, either through the despatch of ground troops or the use of air power, or even to allowing the Bosnians to defend themselves by lifting the international arms embargo that locked in place a Serb advantage in heavy weaponry.

Only a very small number of Conservative MPs, such as Patrick Cormack, Bill Cash and Winston Churchill (junior), supported early military intervention to support the Bosnian government against aggression. The British government felt so strongly about the matter that it not only refused to help the Sarajevo government, but also did everything it could to prevent the Americans from doing so.

The Conservative ministers who led this effort, especially the then foreign secretary, Douglas Hurd, and defence secretary, Malcolm Rifkind, were neither stupid nor heartless. They were convinced that there was no British national interest at stake in Bosnia, and that any intervention would be at best ineffective and at worst mire Britain in an unwinnable "guerrilla war" comparable to Northern Ireland or even Vietnam. "The instinct of the realist," Hurd later wrote, "was to stay out."

To reduce the pressure for action, the government adopted a subtle strategy. The war was turned from a political into a "humanitarian" problem through a relief effort that required a substantial British UN force to protect it; these units later became an obstacle to intervention because London argued that they might be taken hostage by the Bosnian Serbs. The essential distinction between aggressor and victim was obscured in favour of a general moral equivalence.

“This is not a one-sided conflict in which there are white hats and black hats at war," the foreign affairs minister Nicholas Bonsor claimed more than two years into a systematic Serb campaign of ethnic cleansing. Above all, British ministers claimed that the conflict was in essence a "civil war" without a clear aggressor against whom the international community could intervene. In parliament, Tory members of both houses largely echoed these views.

Underlying these positions was a distinct intellectual position that might be termed Conservative pessimist realism. In his very first speech after succeeding Hurd as foreign secretary in the summer of 1995, Rifkind embraced what he took to be Lord Palmerston's dictum that "the furtherance of British interest ought to be the sole object of a British foreign secretary". Hurd warned against the "concept of benevolent international interventionism".

“We have no right, power or appetite," he remarked on another occasion, "to establish protectorates in eastern Europe in the name of a European order." He appealed to the tradition of Edmund Burke - that "anchor of [Conservative] belief" - as an authority against an over-ambitious and messianic foreign policy. The Conservative position was determined not only by diffidence about what Britain could do, but by a powerful hesitation about what it should do.

Instead of supporting the democratic aspirations of the Balkan peoples, London sought the "stability" that only a united Yugoslavia, or even a strong Serbia, could guarantee. It was for this reason that the parliamentary under-secretary of state for foreign affairs, Mark Lennox-Boyd, told the Commons at the start of the conflict in Croatia that "we . . . have a strong preference for the continuation of a single Yugoslav political entity". He saw a role for the Yugoslav army "in restoring order", a phrase that unintentionally gave a green light for the suppression of independence movements.

All this led to a deep rift between London and Washington, where the Clinton administration and many congressional Democrats and Republicans were not only morally outraged by the spectacle of ethnic cleansing, but also fearful that the inability to extinguish a conflagration in the middle of Europe endangered its strategy of "democratic enlargement".

“Bosnia," the US secretary of state Warren Christopher warned in February 1993, "tests our ability to adopt new approaches to our foreign policy in a world that has fundamentally changed. It tests our commitment to nurturing democracy . . . it tests our willingness to help our institutions of collective security, such as Nato, evolve in a way that can meet the demands of the new age." In the end, the US lost patience, and railroaded Britain into an aerial intervention that quickly stopped the Bosnian Serbs in their tracks.

Like all analogies, that between Bosnia and Libya is imperfect, not least because the character of the current crisis is not yet clear. Unlike in the former Yugoslavia, where hundreds of thousands of Muslim refugees were on the move within weeks of the start of the conflict, Colonel Gaddafi has so far not attempted to "cleanse" the opposing civilian population, though he has the means to do so and a track record of extreme violence. In contrast with the poorly armed Bosnian government forces, who were outgunned by the Bosnian Serb militias, Gaddafi's opponents have, to date, more than held their own against the regime.

Yet there are also striking similarities. The wars of the Yugoslav succession were part of a general collapse of communism in eastern Europe, while the Libyan revolt is part of the wave of Arab popular protest that has swept across North Africa and much of the Middle East over the past six weeks. Above all, the mismatch between the lightly armed rebels and the heavy weaponry of the regime makes a massacre possible if the dictator throws off all restraint.

It is hardly surprising to find some Conservatives speaking in language redolent of the Bosnian war. Alan Duncan, a minister for international development, has warned against trying to impose democracy in the Middle East. Speaking of the Gulf autocracies, he argued that the "majority of these rulers are not dictators. These are countries with their own history and cultures. Who are we to lecture?"

As far as Libya was concerned, Duncan argued that, while Gaddafi was bonkers, there should be no outside intervention. More generally, he rejected the idea of a political one-size-fits-all model for the region: "I don't think we want to take military action so women can drive in Saudi Arabia."

Duncan added that the "world cannot be sanitised to the point of perfection . . . you cannot just have black and white. It's always going to be a murky shade of grey." His analysis is surely informed by the mixed experience of bringing democracy to Iraq, but the stress on the "grey" over the black of dictatorship and the white of democracy is also reminiscent of the unwillingness to take sides in Bosnia.

In general, however, the contrast between the Major government's policy on Bosnia and David Cameron's handling of the Libyan crisis so far is striking. Then, the Conservative cabinet, though fractured on almost every other issue, remained united in its opposition to intervention by Britain or any other power. Today, the PM has taken an early lead in calling not only for the "end" to Gaddafi's rule, and freezing of the regime's assets, but also in refusing to rule out military intervention. "We must not," Cameron told a surprised House of Commons, "tolerate this regime using military force against its own people."

For this reason, he announced that he was asking the military and Britain's allies to investigate the establishment of a "no-fly zone", which would serve to reduce the regime's overwhelming advantage in the air. Since then, Cameron appears to have retreated a little from his position, which was criticised as premature by some backbenchers and dismissed as "loose talk" by the US defence secretary. There can be no doubt, however, that putting the subject on the international agenda early seriously hampered Gaddafi's ability to deploy his heavy weapons to strangle the revolt at birth. To that extent, Britain has already intervened.

The Prime Minister's initiative over Libya is embedded in a much broader conception of British foreign policy, which marks a fundamental break from traditional realist positions. To be sure, Cameron explicitly denies being "a naive neoconservative who believes you can drop democracy out of an aeroplane at 40,000 feet". This distinguishes him from the more robust democracy exporters in government, such as the Chancellor, George Osborne, and the Education Secretary, Michael Gove, who reportedly made an impassioned speech in cabinet calling on Britain to support the transformations sweeping the Arab world.

All the same, Cameron's recent Libya speech was much closer to George W Bush's agenda of democracy promotion than the narrow "national interest" focus of Hurd and Rifkind. The Prime Minister broke with decades of British support for "friendly" autocratic regimes in the region. "We need to dispense once and for all with the outdated notion that democracy has no place in the Arab world," he argued. "Too often in the past we have made a false choice between so-called stability on the one hand and reform and openness on the other. As recent events have confirmed, denying people their basic rights does not preserve stability, rather the reverse."

Refusing to be sidetracked into a discussion of the Palestinian issue, Cameron concluded by observing that "some of the more autocratic regimes use the Arab-Israeli conflict as a way of keeping their own populations happy without having democracy". This analysis of the problems of the Middle East is pure neoconservatism, c. 2002.

The overwhelmingly positive response to Cameron's words among Conservatives in the Commons was a sign of just how far the party had travelled from its traditional realist stance. Tobias Ellwood, MP for Bournemouth East, celebrated "a once-in-a-lifetime opportunity to encourage democracy to spread across the Middle East" and called for "an equally robust message for . . . dictators in Africa".

The MP for Halesowen and Rowley Regis, James Morris, argued that “it was in Britain's national interest to . . . promote democracy and support opposition movements where people are moving towards a desire for greater democracy in these countries". Referring explicitly to Bosnia, William Cash, MP for Stone, asked the Prime Minister to consider "properly arming those who are resisting Gaddafi, if necessary, in order to ensure that they are not wiped out, as happened in Srebrenica and Sarajevo".

In all this, Cameron, his cabinet sympa­thisers and the Conservative parliamentary mainstream are much closer to Burke and Palmerston than the "realists" realise. Far from being a cautious advocate of the "national interest", Burke strongly believed not only that “liberty" was "the birthright of our species", but that British interests required its defence, even at the cost of violating state sovereignty. "A more mischievous idea cannot exist," he lamented, "than that any degree of wickedness, violence and oppression may prevail in a country that the most abominable, murderous and exterminatory rebellions may rage in it, or the most atrocious and bloody tyranny may domineer, and that no neighbouring power can take cognisance of either or afford succour to the miserable sufferers."

For his pains, Burke was wearily dismissed by most contemporaries as a fundamentalist ideologue who failed to recognise legitimate French aspirations and the military-political reality that the French Revolution would have to be accommodated. Throughout the 1790s Burke backed a series of failed expeditions to the French coasts on the advice of exiles who had fallen out of touch with the situation at home, or worse still were seen as the agents of a foreign power.

For the moment, however, the Prime Minister's ambition seems more limited than that of Burke. The Irishman demanded all-out war against the powerful Jacobin tyranny of France. Cameron is not yet calling for a confronta­tion with Iran, for example. He more resembles his 19th-century predecessor Lord Palmerston, who was convinced that the defence of British liberties required support for constitutional government abroad. Instead of a long slugging match to impose democracy where it is most resisted, Cameron seems to be aiming for a Bosnian-style strategy of manoeuvre in which relatively small amounts of western inter­vention help to avert a humanitarian crisis, or to tip the balance in favour of a democratic transformation.

Here Palmerston showed the way more than 150 years ago. "Our duty - our vocation," he argued, "is not to enslave, but to set free; and I may say, without any vainglorious boast, or without great offence to anyone, that we stand at the head of moral, social, and political civilisation. Our task is to lead the way and direct the march of other nations. I do not think we ought to goad on the unwilling, or force forward the reluctant; but when we see people battling against difficulties and struggling against obstacles in the pursuit of their rights, we may be permitted to encourage them with our sympathy . . . and even, if occasion require, to lend them a helping hand."

Brendan Simms is professor of the history of European international relations at the University of Cambridge, director of the Centre of International Studies and author of "Unfinest Hour: Britain and the Destruction of Bosnia" (Penguin Books)