It's almost never discussed in the political mainstream. But thousands of foreign troops have now been stationed in Britain for more than 70 years. There's been nothing like it since the Norman invasion. With the 15-month Dutch occupation of London in 1688-9 a distant competitor, there has been no precedent since 1066 for the presence of American forces in a string of military bases for the better part of a century.

They arrived in 1942 to fight Nazi Germany. But they didn't head home in 1945; instead, they stayed on for the 40-odd years of the cold war, supposedly to repel invasion from the Soviet Union. Nor did they leave when the cold war ended and the Soviet Union collapsed, but were invited to remain as the pivot of the anti-Soviet Nato alliance.

A generation later, there are still nearly 10,000 US military personnel stationed in Britain, based in dozens of secretive facilities. Most of them are in half a dozen major military bases – misleadingly named RAF this or that, but effectively under full American control: Lakenheath, Croughton, Mildenhall and Molesworth among others – along with the National Security Agency and missile defence bases such as Menwith Hill in Yorkshire.

British troops are now finally being pulled out of Germany. There is not the slightest suggestion, however, that US forces will be withdrawn from Britain in the forseeable future. But what are they doing here? Who are they supposed to be defending us from?

A clue as to what's at stake was given last week by Robert Gates, a former US defence secretary, when he warned that cuts in Britain's defence spending – still the fourth largest in the world – threatened its "full spectrum" military "partnership" with the US.

He's not the first American official to play on the neuroses of the British security elite, for whom the preservation of a lopsided "special relationship" with the US is the acme of their aspirations for the country. The London establishment's fear of US rejection reached fever pitch last year when parliament finally represented public opinion over military action and rejected what would have been a catastrophic attack on Syria.

Elite anxiety over risking American displeasure or neglect is matched by a growing fear that the British public will no longer tolerate the endless US wars it has dragged them into over the past 15 years. General Sir Nick Houghton, the chief of the defence staff, last month declared that the nation had become "sceptical about the ability to use force in a beneficial way", and must not lose its "courageous instinct". He was echoed by the Commons defence committee, which claimed that "one of the greatest strategic threats to defence" is the public's "lack of understanding of the utility of military force".

No wonder the government has been clamping down on protest rights at bases such as Menwith Hill, a key link in the US missile defence and drone programmes. And it's hardly a surprise that the British public – as in the US itself and other Nato states – has hardened against continued western warmaking, given its record of bloody failure.

Since the post-cold war world gave way to the war on terror, after all, Britain has joined the US in one war of aggression after another – in Afghanistan, Iraq and Libya – with disastrous results. Military operations have been punctuated by campaigns of kidnapping, torture and murderous drone attacks. Nato has morphed from a self-declared defensive alliance into a latter-day colonial expeditionary force, under the cover of increasingly discredited humanitarian rhetoric.

Of course, Britain is very far from unique in hosting US bases. It is part of a global archipelago of American military garrisons, now present in a majority of the world's states: a modern-day empire by any other name. But along with France, Britain is the only US ally still able to "project force" globally and has long played the role of unsinkable aircraft carrier: a US forward base, from which military operations are routinely launched across the globe.

But whose interests are actually served by such a role? No doubt arms contractors are delighted, but it's hard to argue that it benefits the British people – let alone those on the receiving end of the US and British military. Politicians and securocrats claim it gives them influence over US policy, but they struggle to produce the evidence on the rare occasions they're asked to explain how. "The foreign policy elite still have a strong idea," as the Chatham House analyst James de Waal puts it, that intervention based on "values" is an "innate part of what the UK is all about". In fact, what successive governments have done is mortgaged Britain's security and independence to a foreign power – and placed its armed forces, territory and weaponry at the disposal of a system of global domination and privilege, now clearly past its peak.

As was made clear by ministers more than a decade ago, there are now no circumstances in which British governments envisage the use of military force, except in harness with the US. Even Britain's own colonial-era overseas bases, such as Diego Garcia, have long been handed over to the US military, while its inhabitants were expelled. Britain's fake patriots who bleat about the power of the European Commission are more than happy to subordinate the country's foreign policy to the Pentagon and allow its forces permanent bases on British soil.

From the American point of view, its network of intelligence and military bases in Britain may help keep the country tied to the US global network. There's no doubt that would be difficult to disentangle, and there is no shortage of pressure points to discourage even a modest disengagement. The idea of a British Rafael Correa – the Ecuadorean president who closed the US Manta airbase in 2007, saying he'd reconsider the situation if the Americans let Ecuador open a base in Miami – is still political science fiction.

But the withdrawal of British troops from Germany and this year's planned renewal of the US-British defence agreement offer a chance to have a real debate on the US military relationship – and demand some transparency and accountability in the process. There is no case for maintaining foreign military bases to defend the country against a non-existent enemy. They should be closed. Instead of a craven "partnership" with a still powerful, but declining empire, Britain could start to have an independent relationship with the rest of the world.

Twitter: @SeumasMilne