Three years have passed since the British government, in the form of Jack Straw, declared states of affairs in both Darfur and Zimbabwe “unacceptable”. A year later in the case of Darfur this was upgraded to “completely unacceptable”. A feelgood Global Day for Darfur was declared, helped on its way by George Clooney and Elton John. Needless to say, the government accepted what was unacceptable – and has done so ever since.

Today Gordon Brown has decided to stay in bed rather than go to the European Union's Africa summit in Lisbon, thus avoiding the improbable risk of having to smile at Zimbabwe’s Robert Mugabe or Omar al-Bashir, the Sudanese dictator. He has also avoided the recollection that, once upon a time, the word “unacceptable” from a British prime minister would have had boots quaking across Africa. Today all Brown can do at a summit is put his thumbs in his ears, stick out his tongue and say “Boo”.

While diplomats concentrate on being beastly to Mugabe, carnage continues in Darfur and spreads into adjacent Chad. It makes a mockery of the new “liberal interventionism” declared his greatest achievement by Tony Blair, and since endorsed by Brown. In Rwanda in 1994, western powers could at least argue that the massacre took them by surprise. No such excuse is available in Darfur. The horror has been unfolding in full view of the world for three years.

The interventionists have hollered and abused and seized microphones and achieved nothing. The Sudan government’s Arab Janjaweed irregulars, aided by air support, have continued with killings. This has been in response to a separatist rebellion similar to that which was partially successful in southern Sudan, resolved in 2002.

In Darfur some 300,000 people have been massacred, 2m driven into exile and 4m left dependent on western aid in a network of more than 60 refugee camps. Servicing these camps, according to Oxfam’s Alun MacDonald, is now more dangerous “than at any time since the entire conflict began, by a considerable way”. Aid convoys are attacked, aid workers killed and agencies may soon have to withdraw, precipitating a medieval migration across the Sahara.

An inadequate African Union force of 7,000 has proved unable to cope with a renewed Janjaweed onslaught, complicated by feuds between the rebel groups. This force is enhanced by a 26,000-strong United Nations army, deploying with excruciating slowness because Khartoum objects to it containing non-Africans.

All comment on the UN force regards it as too late, too small and too ramshackle to halt what is a raging civil war across a territory the size of France. It has not one helicopter out of its supposed complement of 24. Last week the British Foreign Office bleakly offered to hire a few from a private contactor, if they could be found. This intervention, stimulated by the West, has failure already built-in.

Gesture diplomacy has boosted the self-righteousness of the Khartoum regime on the one hand and encouraged the rebels, now split into a dozen factions, on the other. As a result the rolling autonomy accepted in the south has not taken root. Rebels walked out of the last peace talks.

While comparing horrors is odious, Darfur should outrank Afghanistan or Iraq as a cause for intervention. It ticks the boxes of Blair’s Chicago speech on the use of military force. There is an ongoing human catastrophe. There is a sovereign government apparently to blame. The whole region is inflamed. The UN has called for action in innumerable resolutions. Darfur is more open and shut even than Kosovo.

So why are Britain’s macho interventionists suddenly so timid? Why are they not summoning troops to the flag as in Yugoslavia, Afghanistan and Iraq, and instead falling back on limp condemnations and armchair diplomacy? It is hard to avoid the conclusion that Darfur is Africa and that to western interventionists black people matter less than whites or browns.

A small job such as Sierra Leone can be handled, but Sudan is a desert land of which they know little. Europe’s frontier in former Yugoslavia is worth shedding British blood, as are the oilfields of Mesopotamia and the old imperial borders of the Punjab. Africa is different, even the Africa over which, in the case of Sudan, Britain once ruled with credit. Words must suffice.

There is, of course, a subplot here. The motive behind the Lisbon summit is somehow to rescue Europe’s former “backyard” custodianship of Africa at a time when China, Russia and India are being welcomed with open arms. In November last year the China/Africa summit of 45 nations in Beijing celebrated a tenfold rise in China’s trade with Africa.

Britain can boss dictators in the Muslim world but oil-rich Africans are increasingly disinclined to kowtow to the West. Since the end of colonialism, African states have suffered two ideological imports from Europe, aid-rich socialist planning and aid-rich IMF/World Bank free-marketeering. Both have impoverished most of the countries on which they were imposed. Yet still they are lectured on failed governance and corruption – from the EU of all hypocrites.

Chinese diplomats do not tell African dictators of their “unacceptability”. They do not threaten to arrest their ministers and haul them before the International Criminal Court for war crimes. They do not hector Mugabe or demand that Bashir accept UN troops. They just want to buy oil.

The EU in Lisbon appears in supplicant mode. It lets its bluff be called on Mugabe’s travel plans and declares Africa the “equal” of Europe. Jose Manuel Barroso, the EU president, patronises the absent Brown by saying that leadership requires “being prepared to meet people your mother would not like to meet”. This comes from an EU apparat that would sell its mother into slavery rather than risk an African boycott of Lisbon and thus endanger its most cherished perk, a lavish junket at our expense.

Neither Britain nor any western state will intervene in Zimbabwe or Sudan in the only way that might make any difference, by military force. On this point Blair in Kosovo was right: armchair intervention is cynical, ineffective and probably counter-productive. Those who wish to change a foreign government, for whatever reason, must be ready to fight. You cannot, as Kipling said, sing Rule Britannia and go “killing Kruger with your mouth”. Regime abuse is not regime change.

Modern Britain is so lacking in global clout that it cannot even persuade Europe to make Mugabe stay at home or shame Khartoum into respecting the innocence of a British teacher. What hope is there that London might change the dynamic in Khartoum or Harare?

In 1916 the British drew the borders of strife-torn Sudan, embracing once-autonomous Darfur. For years it flattered and subsidised Mugabe. Africans are now reaping what Britain sowed but there is nothing London can do since it is recklessly overextended in Basra and Helmand. It would do most good by shutting up.

Alex de Waal, historian of Darfur, describes it as displaying “the basic pattern of grievances shared by all the world’s marginalised peoples”. Its miserable and intractable conflict will be resolved only when the finally exhausted parties agree to peace. This is currently prevented “by the perfidy and ruthlessness of the Sudan government and the incompetence and vanity of the armed movements”.

For four years the West has cried: something must be done, action must be taken, troops must be sent. What and by whom is not stated. Ever since the UN, goaded by America and Britain, abandoned its former respect for national sovereignties, nobody has defined liberal intervention as anything but a jerking of the knee. Worse, the examples of East Timor, Bosnia, Kosovo, Kurdistan and now Darfur suggest that any separatist movement is well advised to resort to arms and atrocity to secure western sympathy or support.

Global policing has strayed far from the goal of defending borders and organising humanitarian aid. By extending its remit to the internal politics of states, liberal intervention is becoming an enemy not a friend of peace. Lacking imperialism’s permanent commitment to a conquered land, it has become a half-hearted meddling in the affairs of others. It is the ideology of the fidget.

simon.jenkins@sunday-times.co.uk

Times Recommends

• We have kit and leadership. Let’s go
• Behind the scenes at the biggest deal
• Conferences — what a waste of money