Sleeping with the enemy - or rather, living, working and to some extent suffering with them - is always a complicated business morally speaking.

Having just got back to London from my three months in Belgrade, I have been going through the post which has accumulated for me.

Some letters were very kind, but there was plenty of hate mail from people who didn't want to be told what it was like being on the receiving end of Nato's bombing.

Time and again they built up to their final clinching argument: would the BBC have had a correspondent in Berlin during the Second World War?

Answer: Absolutely - if only we had been able to.

John Simpson reports from Belgrade

Personally, I cannot see the problem with wanting to know more about what is going on rather than less. It seems to be the entire point of broadcast journalism.

But what these people really dislike is the reminder that under the bombs there are men and women like themselves. It is unsettling; it muddies the moral waters.

They do not want to know what is being done in their name. In Belgrade I came to think of this as a specifically Serbian attitude - it was only when I went through my post back in London I realised it was a more generally human one.

Tribal sensitivities

The people who live in the former Yugoslavia, with its dozens of nationalities, quite possibly possess more racial awareness than anyone else on earth.

Where you come from, who your parents were, explains everything. Having spent millennia typecasting everyone in tribal terms, the people of the area were suddenly forbidden even to mention their tribes during the 35 years of Marshall Tito's rule, after which the racial consciousness burst out again with hugely increased force.

Serb electricity technicians have their work cut out repairing Belgrade facilities

Ever since the slow violent break up of the old Yugoslavia began, I have watched the spread of this deeply depressing process.

It is the final reductionism. You are not an individual - you are merely the sum of your genes, to be regarded as a friend or an enemy accordingly.

Time and again when I was in Belgrade I found myself getting into arguments.

"You're bombing us," people would say. I would point out that they were not being any more bombed than I was.

But of course they did not mean me as an individual, they meant me as the representative of a tribe that was bombing their tribe, and it is much easier to do unpleasant things to a representative than to an ordinary living person with an individuality of his or her own.

'Albanians did not count'

I got to know a particular middle-aged woman quite well while I was in Belgrade. She was deeply angry about the bombing and liked to tell me in some detail about the suffering Nato was inflicting.

One day as I came into the room I could hear her laughing with one of her Serbian friends. That was quite unusual and I could see that something must have happened. She quickly turned serious.

Serbian children just outside Belgrade give the traditional three-fingered salute

"It's awful," she told me in her 'look what you people have done now' sort of way. "Nato has bombed a column of Albanian refugees." That was what had been making her happy. Hitting Albanians did not count - only Serbs counted.

The most interesting and significant thing that happened to me in my three months in Belgrade was when I fell down and ruptured my left thigh muscle. It was quite serious and I needed an operation quickly.

The ambulance drove me to a nearby hospital and as I lay on the stretcher in some pain, one of the paramedics started railing at me about Nato and Tony Blair and the bombing.

The doctors themselves were charming and friendly and in spite of the power cuts and a continuing air raid, they operated on me extremely well, especially given the shortages of medicine and equipment thanks to UN sanctions.

I later became friendly with one of the surgeons. But it was only as I left Belgrade the other day that he told me how some of his colleagues had criticised him for looking after me.

"You should have refused to treat him," they had said. Tribalism can be more important than anything, even than the Hippocratic oath.

Poignant memories

Difficult though it can be, especially at a time when we are discovering how abominable the sufferings of ethnic Albanians in Kosovo have been, I learned a new affection for the Serbs.

The people here who sent me the hate mail will probably say I was a victim of the Stockholm syndrome, whereby prisoners come to love their captors.

I prefer to think it was because I learned a little fellow feeling. Lying in my hospital bed for instance, through the long hours of darkness, with the sound of Nato planes overhead and the bombs falling - knowing that they had already hit my hospital once by mistake - listening to the other patients groaning or calling out in their sleep or shouting "Sister" for the one overworked nursing sister who had to look after 50 people, I knew we were all in this together.

If a bomb had hit the hospital in the nights I was there, we would have all suffered - the English patient, along with the Serbian ones. When it really counts, your tribe does not mean anything.