Pragmatism sometimes dictates that British ministers and civil servants need to speak with representatives of the world's least pleasant regimes: Robert Mugabe of Zimbabwe, Colonel Gaddafi of Libya, President Ahmadinejad of Iran, for example. The same applies to King Abdullah of Saudi Arabia. After all, the desert kingdom contains more than one-quarter of the world's oil reserves, more than 20,000 Britons work there and, in the UK, many more rely on Saudi orders. Saudi Arabia also holds an important strategic position in the fragile powder keg of Middle East politics. Genuine British-Saudi two-way trade and co-operation are welcome.

That does not mean that Britain has any business to be offering King Abdullah the accolades of a red-carpet welcome and a lift to Buckingham Palace in a golden carriage, followed by a state banquet for 200 people, all at taxpayers' expense. What sort of message does this send out about a regime characterised by public floggings and executions, the prolonged detention without charge and routine torture of peaceful critics, trials that are an affront to justice and women kept virtually prisoners in their own homes? One of those protesting outside the palace will be Sandy Mitchell, a Scottish hospital technician, who was imprisoned on false pretences and tortured by Saudi police in 2000. Only the Liberal Democrats will have the decency to join him. Meanwhile, Gordon Brown and David Cameron have not even committed themselves to raising the human rights issue, preferring weasel words about minor reforms and common interests. The "ethical dimension" to foreign policy, pledged by the late Robin Cook when Labour came to power in 1997, appears to be an optional extra. What is the difference between our Prime Minister boycotting a conference being attended by Robert Mugabe and honouring King Abdullah? The answers are defence contracts, security and oil.

This is morally repugnant. Last year the British government in effect allowed the Saudis to persuade it to pressurise the Serious Fraud Office to drop an investigation into the alleged bribery of Saudi officials by the British company BAE systems. Though the official reason was "safeguarding security", at stake was a new order from the Saudis for fighter aircraft. Britain's pursuit of trade should never be at any price.

As regards security, King Abdullah this week accused Britain of failing to act on Saudi intelligence that could have prevented the 2005 London bombings. While this claim deserves investigation, it appears unlikely that the Saudi information was specific enough to have averted tragedy. It is true that western interests would be undermined if the House of Saud were to be toppled by anti-western Islamic militants. But by propping up a medieval, anti- democratic regime that appears incapable of anything more than gestural reform, we simply fan the flames of fanaticism in the desert kingdom.

If there is one lesson from this sad saga, it is that Britain must work towards weaning itself off Saudi oil. This should colour policy on renewables and, possibly, nuclear power as well. Meanwhile, the government has no business to be honouring the Saudi royal family.