While few people would expect every government policy to precisely reflect majority public opinion, it is hard to see what is democratic about a British foreign policy whose very fundamentals – agreed by both Labour and the Conservatives – are consistently opposed by voters.

Britain is not a totalitarian state. It has regular elections and free speech, and its citizens have the freedom to organise politically. So how is it that such a democratic deficit exists when it comes to the country's role in the world?

In February 2003, more than 90% of Britons opposed Tony Blair's government joining the invasion of Iraq in the absence of a second UN resolution. As we know, the invasion went ahead the following month without such a resolution being passed.

Three years later, 63% thought Blair had tied Britain too closely to the Bush White House. In the same poll, 61% opposed the assault on Lebanon that Israel was undertaking at that time – an assault that was nevertheless effectively supported by Britain.

At present, both main parties plan to renew the Trident nuclear system, despite opposition from 63% of voters. Fifty-four per cent of Britons express support for the rule of international law yet, last week, Gordon Brown's government began discussing "safeguards" to exempt suspected war criminals from the reach of British courts.

The de facto purpose of Britain's foreign policy has traditionally been to advance the interests of various concentrations of social and economic power, not to reflect the will of the voting public. Above all, it is the commercial interests of those best placed to influence the government that tend to be prioritised by policymakers. This in turn is why Britain has supported the US-led maintenance of a global system seen as amenable to those commercial interests, and tried to maximise Britain's influence within that system.

This picture needs to be placed in an historical context. While we think of globalisation as a recent phenomenon, its roots go back to the imperial age of the 19th century.

Then, Britain presided not merely over an empire but over a global trading system, lubricated by credit from London's banks, underwritten by its insurers, and imposed on weaker nations by military force.

The devastation wrought by the calamitous years of 1914-1945 dealt a fatal blow to the country's capacity to perform this global management role. The task was inherited by the US, whose view of how the world should be organised economically and politically was broadly consistent with that of British elites.

London therefore sought to protect its economic power and international status by placing itself close to Washington. The instruction given by Blair's chief of staff to Britain's ambassador to the US, Sir Christopher Meyer, to "get up the arse of the White House and stay there", was an expression of that longstanding policy.

At a time when taxpayers face spending a generation paying off the gambling debts of the City, the disproportionate influence of wealth over policymakers is not a difficult concept to understand.

This influence is exerted in myriad ways – some obvious, some less so. Wealth is power. It buys lobbying consultants, concentrates the minds of politicians in need of campaign donations, owns most of the media and is generally well-placed to make life easy or difficult for government depending to what extent its needs are being met.

The dividing line between public and private interests is in any case far from clear. In a country with low social mobility, people in positions of state or corporate power are disproportionately likely to have come from wealthy backgrounds, and to have internalised the general values and outlook associated with that background. The interests of this elite are diverse but broad consistency exists, and sets the framework for how the country is governed.

The public-private boundaries are particularly blurred when it comes to foreign policy. As Anthony Sampson noted in his recent study of power in modern Britain, Who Runs This Place?, "many [British] embassies now include temporary 'secondees' from big corporations, including BP, Shell, banks and construction companies, who pay their salaries".

Two years ago the Guardian reported that "the chief lobbyist of Britain's biggest arms company [BAE Systems] was given an official security pass allowing him to wander freely around the Ministry of Defence". Access comes at all levels. Sampson quotes former foreign secretary Robin Cook saying BAE's chairman "appeared to have the key to the garden door to No 10", and that "certainly I never once knew No 10 to come up with any decision that would be incommodating to British Aerospace".

Of Washington's influence over Whitehall there is much that can be said, but one aspect is perhaps more telling than most. Britain's retention of an "independent nuclear deterrent" is probably the most obvious example of an attempt to bridge what the historian Paul Kennedy called "the divergence between Britain's shrunken economic state and its overextended strategic posture". Yet British nuclear weapons have always been reliant on US management and technology.

The effect of this longstanding dependency is, in the words of Prime Minister Harold Macmillan's permanent secretary, Sir Robert Scott, to "put us in America's pocket". It is reasonable to assume that the 2004 renewal of the US-UK Mutual Defence Agreement was one factor in the minds of policymakers during the early years of the "war on terror" and in the run-up to the invasion of Iraq.

These are just some of the pressures that crowd the public's voice out of decision-making. Locating power and mapping influence with real precision is a complex task in relatively open societies like Britain's, and this article provides just a snapshot. Nevertheless, evidence of a serious democratic deficit in British foreign policy is reasonably clear. What remains then for the public is a choice: accept marginalisation, or use our political freedoms to change the balance of power.