On the nauseating political doublespeak scale, David Cameron's claim to "support the Arab spring" on a trip to sell weapons to Gulf dictators this week hit a new low. No stern demands for free elections from the autocrats of Arabia – or calls for respect for human rights routinely dished out even to major powers like Russia and China.

As the kings and emirs crack down on democratic protest, the prime minister assured them of his "respect and friendship". Different countries, he explained soothingly in Abu Dhabi, needed "different paths, different timetables" on the road to reform: countries that were western allies, spent billions on British arms and sat on some of the world's largest oil reserves in particular, he might have added by way of explanation.

Cameron went to the Gulf as a salesman for BAE Systems – the private arms corporation that makes Typhoon jets – drumming up business from the United Arab Emirates, Saudi Arabia and Oman, as well as smoothing ruffled feathers over British and European parliamentary criticism of their human rights records on behalf of BP and other companies.

No wonder the prime minister restricted media coverage of the jaunt. But, following hard on the heels of a similar trip by the French president, the western message to the monarchies was clear enough: Arab revolution or not, it's business as usual with Gulf despots.

The spread of protest across the Arab world has given these visits added urgency. A year ago, in the wake of the uprisings in Tunisia and Egypt, it seemed the Gulf regimes and their western backers had headed off revolt by crushing it in Bahrain, buying it off in Saudi Arabia, and attempting to hijack it in Libya and then Syria – while successfully playing the anti-Shia sectarian card.

But popular unrest has now reached the shores of the Gulf. In Kuwait, tens of thousands of demonstrators, including Islamists, liberals and nationalists, have faced barrages of teargas and stun grenades as they protest against a rigged election law, while all gatherings of more than 20 have been banned.

After 18 months of violent suppression of the opposition in Bahrain, armed by Britain and America, the regime has outlawed all anti-government demonstrations. In western-embraced Saudi Arabia, protests have been brutally repressed, as thousands are held without charge or proper trial.

Meanwhile, scores have been jailed in the UAE for campaigning for democratic reform, and in Britain's favourite Arab police state of Jordan, protests have mushroomed against a Kuwaiti-style electoral stitchup. London, Paris and Washington all express concern – but arm and back the autocrats.

Cameron insists they need weapons to defend themselves. When it comes to the small arms and equipment Britain and the US supply to Saudi Arabia, Bahrain and other Gulf states, he must mean from their own people. But if he's talking about fighter jets, they're not really about defence at all.

This is effectively a mafia-style protection racket, in which Gulf regimes use oil wealth their families have commandeered to buy equipment from western firms they will never use. The companies pay huge kickbacks to the relevant princelings, while a revolving door of political corruption provides lucrative employment for former defence ministers, officials and generals with the arms corporations they secured contracts for in office.

Naturally, western leaders and Arab autocrats claim the Gulf states are threatened by Iran. In reality, that would only be a risk if the US or Israel attacked Iran – and in that case, it would be the US and its allies, not the regimes' forces, that would be defending them. Hypocrisy doesn't begin to describe this relationship, which has long embedded corruption in a web of political, commercial and intelli gence links at the heart of British public life.

But support for the Gulf dictatorships – colonial-era feudal confections built on heavily exploited foreign workforces – is central to western control of the Middle East and its energy resources. That's why the US has major military bases in Kuwait, Qatar, the UAE, Oman and Bahrain.

The danger now is of escalating military buildup against Iran and intervention in the popular upheavals that have been unleashed across the region. Both the US and Britain have sent troops to Jordan in recent months to bolster the tottering regime and increase leverage in the Syrian civil war. Cameron held talks with emirates leaders this week about setting up a permanent British military airbase in the UAE.

The prime minister defended arms sales to dictators on the basis of 300,000 jobs in Britain's "defence industries". Those numbers are inflated and in any case heavily reliant on government subsidy. But there's also no doubt that British manufacturing is over-dependent on the arms industry and some of that support could usefully be diverted to, say, renewable technologies.

But even if morality and corruption are dismissed as side issues, the likelihood is that, sooner or later, these autocrats will fall – as did the Shah's regime in Iran, on which so many British and US arms contracts depended at the time. Without western support, they would have certainly been toppled already. As Rached Ghannouchi, the Tunisian leader whose democratic Islamist movement was swept to power in elections last year, predicted: "Next year it will be the turn of monarchies." When that happens, the western world risks a new backlash from its leaders' corrupt folly.

Twitter: @SeumasMilne