More than twenty years ago Bob Geldof and I shared what turned out to be a case of wishful thinking.

We believed that the millions of pounds raised by Band Aid in a response to the famine that was wracking Ethiopia would go towards ensuring that never again would we look at our television screens and see emaciated figures, the consequence of famine, dying.

Since then, as Africa's crisis has deepened, Bob Geldof and I have gone our separate ways. The Irish rock star, businessman and philanthropist has continued to devote many of his energies to African causes, from membership of the British government's Commission for Africa to a leading role in organising the Live Aid concerts that accompanied the G8 summit in Gleneagles in July 2005. And he collected a knighthood along the way.

Geldof, then, is a pioneer of Celebrity Aid, though in seeking to draw the rich world's attention to the plight of the African poor, even this larger-than-life character stands on the shoulders of earlier figures such as Danny Kaye, the first ambassador for the United Nations Children's Fund [Unicef] in 1954.

Since Geldof's Ethiopian epiphany in 1984, more celebrities have joined the cause of Africa's recovery, from Kate Moss to Bono, Angelina Jolie to Chris Martin. Now they have been joined by Madonna (and her film-director husband Guy Ritchie), whose adoption of a boy from Malawi has created a media furore.

Sir Bob himself has helped raise more for Africa through Live Aid, and saved the continent's governments further huge sums by throwing his weight behind debt relief for some of the world's poorest countries. More than that, he has kept Africa's crisis high on the international agenda - or at least higher than it otherwise would have been - through ceaseless lobbying, a powerful personality and deep compassion.

All this while, I have done little more than send back to the Financial Times increasingly sceptical reports from Africa's development frontline about the benefits of aid, and questioned the role of the thousands of foreign-based or foreign-funded non-governmental organisations (NGOs) that have proliferated across the continent.

And now, a generation after our Ethiopian experience, I find it hard to find much we agree on.

I believe that debt relief without the toughest of conditions will fail; that to provide more aid is to send good money after bad; and that although the report of the Africa commission on which Geldof served is an invaluable source of information, it failed to address the fundamental question about the failure of aid.

The trap of cynicism

Like the poor, celebrities have always been with us. And as long as Africa remains a scar on the conscience of the west, as somebody once said, I expect they will stay with us. On either side of this great divide of life-experience and life-chances, this is one area where there is no prospect of any supply problems.

The celeb phenomenon has been around as long as the African continent has been in trouble; but it has increased in velocity since the problems of poverty, illness and dependency became more broadly exposed to the world's eyes in the first decades after independence.

As Hollywood's A-list finest such as Audrey Hepburn have been supplemented by a far wider range of figures from the worlds of pop music, television and football, as well as film, there is as much chance of stopping the southward flow of glamour as there is of finding a quick fix for Africa.

For there is a lot to keep these celebs busy. At least 40% of the continent's 800 million people go to bed hungry each night. What is more, as the world hunger report published in October 2006 revealed, this number is increasing each year. Some 3 million African children die every year of preventable diseases before they reach the age of 5.

And that is just the human toll. The loss of biodiversity as a result of soil depletion, desertification, and forest clearance has meant that dozens of animal species have become endangered or extinct - creating a further space for conservationist celebs to enter and campaign to save favourite (and very often the most photogenic) creatures.

There are occasions when the accompanying media coverage - designed to entertain as well as raise concern among potential western aid-givers - is plainly insensitive and silly, as when Kate Moss "blacked up" for the Independent's special Africa supplement (though the blame falls as much on the journalist who thought it up as the model who went along with it). It is true too that some events or photo opportunities owe less to a compassionate heart than to attempts to boost a flagging career.

It also seems to me, however, that the frequent mockery and derision by journalists and others of Bono, Geldof, Madonna or any of the other celebs is insufferable arrogance. To say that they are motivated by a desire for further publicity, or that they are expressing their concern in an inappropriate way, is unwarranted.

The vice of aid

But it is possible to have concerns without falling into fashionable cynicism. I have three such.

First, there is a danger that the attention given to celebrities' involvement is a distraction from the debate that shouldbe taking place: about the fact that aid does not work in Africa.

That is surely beyond doubt. In Kenya, recipient of hundreds of millions of dollars in aid since independence in 1963, more of its citizens than ever are categorised as impoverished - around 55-60% - than when the flag of statehood was raised and Jomo Kenyatta installed as the country's founding president. True, life-expectancy has increased (though I suspect it is starting to decline), but an increase in longevity is scant return on aid investment if in other respects, life for millions of Kenyans remains nasty and brutish.

In this respect, there is surely the danger that those in the business of aid have lost sight of the purpose of aid.

The second, related concern is that the publicity surrounding celebrities tends to obscure discussion of whether aid has contributed to - or in some cases evencaused - Africa's problems.

Kenya's northeast, where aid has subsidised the settlement of people on land that never had the capacity to sustain them, is one prime case. Another is Sudan in the late 1980s and early 1990s. There, the United Nations programme to feed civilians caught in the country's north-south civil war (Operation Lifeline, established in April 1989) arguably did as much harm as good, by taking responsibility from the shoulders of the men who were leading the fighting.

Year after year food aid poured in to Sudan, until the process became institutionalised and the "aid" became an integral part of the wider conflict. A tough question was avoided: should the donors have in effect declared a cut-off point in the delivery of food aid, in order to try to concentrate the protagonists' minds on the peace process?

This would have been a terribly difficult decision to make, and if it had been it is certain that TV cameras would be present to record the last breaths of stick-limbed children. But the decision would have been no more difficult, nor more terrible in its consequences, than one to take a country into war.

The third concern is that the alliance of celebrity involvement and aid strategy in Africa is diminishing, or will diminish, the continent's self-confidence.

A post-independence generation of Africans says it does. From Andrew Rugasira, the Ugandan coffee entrepreneur, to John Githongo, the exiled anti-corruption campaigner from Kenya, to Moeletsi Mbeki, a leading South African businessman, comes the same answer: we don't need aid, we want a fair crack of the trade whip.

Part of their concern is the impact of aid on the role and the capacity of the state. Kenya (to stay with the example of the east African country, so long considered - though not any more - as one of Africa's relative "success stories") has been a food importer most years. I expect it always will be. Certainly the trend is not encouraging: the population has doubled since 1980, two-thirds of the country is arid or semi-arid, and the size of the averageshamba (small farm) has fallen by half since the 1970s.

I don't doubt that many people - more than a million - are going hungry in northern Kenya. But questions must be asked that tend to be evaded:

• why are there so many people living in such an inhospitable part of the country in the first place?

• has a population that was dominantly nomadic become settled? If so, how has it survived?

• has donor aid unwittingly created or contributed to the problem that is entrenched or endemic?

• will hunger continue, despite conventional aid efforts, as the years go by - and will there be more mouths to feed?

And even more critically:

• is the donor/NGO presence doing more harm than good?

• are aid donors, by taking on a responsibility for care, contributing to the atrophy of the Kenyan state, thus leaving it less and less capable of meeting its obligations to its citizens?

If the answer to the last two questions in particular is yes, even a heavily qualified yes, it should be followed by a question which goes to the heart of the billion-dollar development failure in Africa:

• could the experience of northern Kenya provide insights that lead to a better understanding of the weakening of the state across Africa?

For - to explain the last point - if the state cannot deliver its side of the contract (provision of basic services including roads, healthcare, security and law-enforcement, and disaster relief) why should the citizen stay loyal? Why pay taxes - and ultimately, why not bribe? And as the state recedes, why not turn to regional and ethnic loyalties, or to the political "big man"?

The air of debate

What then should be done? The answer is not to scorn the celebs but to encourage them - precisely to initiate a much-needed debate on these three issues.

Just imagine if Bono said: We should be prepared to admit defeat and re-engage - but re-engage on differentterms. The process - of disengagement and re-engagement in turn - should take place over ten years. At the end of those ten years, any aid project should be conditional on matching funds from African sources.

Or if Bob Geldof declared that: Africahas capital tied up in land - so radicalfooking reform of land tenure isfooking essential.

Or if Roger Moore maintained that:Africa's ill-managed state pension-funds should be opened up to competitive managements.

Or if Madonna argued that: We should respond to the fact that the diaspora of Africa's educated is swollen by 60,000 a year. This has led to the bizarre, outrageous situation that more doctors who were trained in Malawi are practising in England's second city of Birmingham than in Malawi itself. If one of Malawi's main exports is health professionals, that is not in itself a bad thing - what is unacceptable is that there is no organised replenishment. But if visas cost the equivalent of what it costs to train them in the first place, and the money is spent on the schools and universities that produced them, Malawi could thrive.

If these and other celebrities made such statements - in tune with modern African realities and the lessons of the past forty years, rather than with the outdated nostrums of the aid industry - the result would be an opening of a space for discussion of Africa's real needs.

Whether the celebrities can say these things - or whether their armies of advisers and publicists and sponsors will allow them - we can all agree on one thing. To provide effectiveaid, as opposed to a response to a humanitarian appeal, and to ensure that it contributes to a self-sustaining recovery, is a difficult thing to achieve. Who better than celebrities to boost a debate on ways to do it?