John Holmes had what many would regard as the worst job in the world.

A senior British diplomat, in 2006 he was persuaded by Tony Blair to become the United Nations emergency relief co-ordinator for humanitarian operations across the world. From Darfur to Gaza, Sri Lanka to Congo, he spent his waking life in the world's most desperate trouble spots trying to prevent ordinary people from paying the ultimate price for the venality and stupidity of their governments. You wonder how he remained sane.

He did so by falling back on the detachment that career civil servants acquire through overlaying intractable problems with committees and acronyms, policy initiatives and outcome agreements. The bureaucracy of disaster you might call it. "One of the innovations during my time as ERC," he remarks proudly, "was the establishment of a Security Council Expert Working Group on POC." You need to keep flipping back and forward to the glossary to understand what he's on about.

Sometimes it leads to an almost Monty Pythonesque bathos. While trying to find some way to prevent the Israeli Defence Force from massacring the 1.5 million Palestinians in the Gaza refugee camps with phosphorous weapons, bulldozers and depleted uranium shells, he remarks: "All in all, Israeli tactics did not seem to outside observers like myself to be well thought through or effective." Well, you could say that again.

However, I'm sure he did very good work. The problem with humanitarian intervention is, surprisingly, a largely bureaucratic one. There is usually enough money around – £12 billion spent between 2005 and 2010, 90% of which came from a dozen Western governments including ours. And there seems no shortage of people available to help, organised by a plethora of NGOs (non governmental organisations) such as Oxfam, Concern, Care, Save The Children, Medecins Sans Frontieres. You get the impression of gangs of aid workers jostling each other for a piece of the humanitarian action. The biggest problem is to stop them falling over each other and creating confusion, as appeared to happen in the biggest disaster of recent times, the Asian tsunami of 2004, which led to the creation of the post of emergency relief co-ordinator.

However, there is little that even the most organised and co-ordinated relief effort can do with wars. Seventy per cent of humanitarian aid goes to the victims of conflict, and here people like Holmes come up against the real problem, which is, of course, politics. It is almost impossible to prevent the humanitarian aid effort becoming highly politicised, because of Western governments trying to promote their diplomatic objectives, or local warlords looting food and supplies. Sometimes, Holmes admits, humanitarian aid can prolong wars simply by keeping more people alive.

He believes that, if people just took a bit more time to talk through their grievances, and stop seeing everything in black and white, everything would be a lot better. And it is very hard to disagree with him. "I have no silver bullets," he says, "but if there is one thing I would offer it is the need to understand the roots of conflict and political problems in all their complexities." To which the only answer is, well, yes. If the world were run by British diplomats, then I'm sure it would be a better place.

There is, however, the small problem of the illegal war in Iraq, launched by his boss, Tony Blair. This began as an extension of the kind of humanitarian interventionism that had been employed in Kosovo and Sierra Leone, but it turned into Britain's worst foreign policy disaster since Suez. Where were the British diplomats then? Well, actually, Holmes was at the heart of the action as ambassador to France at the time when Tony Blair's cronies were lambasting the French as cheese-eating surrender monkeys for insisting that there should be that second UN resolution before invading Baghdad.

Iraq turned into one of the worst humanitarian disasters of modern times, with 100,000 dead and millions displaced – but Holmes is silent about all this. He hints at his view in the chapter on Afghanistan and Pakistan when he says: "I wish Western governments could come to a more nuanced view of local security and political issues rather than a Manichean perception of good and bad action, over-influenced by the war on terrorism." I'm sorry, but nuance isn't really something that political leaders such as Tony Blair and George Bush deal in.

There is something in Holmes's moderation and reasonableness that is slightly chilling. He is very honourable, and I'm sure he has done a very good job, with his 300,000 miles of travel to 43 countries. He makes important observations about how climate change is likely to be the main humanitarian front in the next half century, and about how the International Criminal Court can sometimes make peace talks more difficult by giving no way out for leaders such as President Bashir in Sudan. But there is a worrying complacency, an inability to recognise that even reasonable and "nuanced" people like John Holmes can play their part in creating humanitarian disasters, without even being aware of it.