I HAVE heard countless people here, in the North of England, say over the last few days that they cannot comprehend what is happening outside the Holy Cross school in Belfast.

Of course, it is difficult for anyone to understand such barbaric behaviour, directed at innocent four-year-old children on their way to school.

But, sadly, as someone brought up in Northern Ireland, I know something of the deep and ugly divisions, going back many generations, which lie behind the shocking and sickening scenes we are witnessing today.

These clashes have nothing to do with religion and everything to do with bigotry. As the Holy Cross school itself highlights, this is a society where Protestants and Catholics go to separate schools.

They live on different estates, drink in different pubs, eat in different restaurants, even work in different factories. They may be the same colour and worship the same God, but, at times, they may as well be from different planets.

Northern Ireland is changing. But in many of the tougher, hard-line areas Protestants and Catholics still rarely meet. Families on both sides will have suffered throughout more than 30 years of violence and intimidation. They mistrust, fear and simply do not understand each other.

Those vulnerable four-year-olds at Holy Cross School are victims, not just of the appalling violence we have seen this week, but of this depressing cycle of division and hatred that, despite all the progress made in Northern Ireland in recent years, has, in too many areas, lingered and endured, passed down from one generation to the next.

Those bitter protestors and angry parents pictured at each others' throats outside Holy Cross have been through the same segregated education system their children are now joining. Like me, many were schoolchildren in the 1960s and 1970s, and will remember when the violence started.

Ours was one of just a few Protestant families living in a Catholic border town, badly hit by the Troubles. At school, my friends were Protestant, living in outlying villages where the kerb stones are painted red, white and blue and the Union flag flies from every other telegraph pole.

In town, my friends were Catholic, living on estates where the kerbs are green, white and gold - the colour of the Irish tricolour - and huge murals depicting IRA gunmen and anti-British slogans fill gable-end walls.

Our secondary school bus was often stoned or blocked by barricades as it travelled through Catholic streets. At one stage, in the 1970s, our school was plagued by bomb threats. At times, including the middle of my GCSEs, we were given just a few minutes to evacuate the building.

I became used to being called names by both sides. When I was out with my Catholic friends, other Catholics would brand me a "Limey (British)-lover" or "Jaffa" (a name, linked to Orangemen, for Protestants). I remember one girl telling me she had never met a Jaffa before: "I thought you all had two heads".

More extreme Protestant youths would accuse me of being a "Fenian or Taig-lover" (abusive terms for those who befriended Catholics). These were people who regarded the Pope as the "anti-Christ" and Ian Paisley their hero.

I, and my brothers and sisters, had our feet lodged in both camps, which was difficult. There were enough bombings, shootings and riots to remind us that these extremists weren't playing games. Apparently, idle threats could easily become an ugly reality.

One of my older sister's Catholic friends fell for a British soldier and was dragged from her home in the middle of a riot and "tarred and feathered" - a frequent punishment for those who stepped out of line. She was tied to a lamppost before having her head shaved and covered in tar and feathers.

My older brother fell in love with a Catholic girl. Neither family was pleased. There were known IRA members on her side, one in jail for terrorist offences. Two of our cousins had been shot dead by the IRA, other family members were in the security forces.

There was suspicion and mistrust on both sides. This was a real-life Romeo and Juliet being acted out on the streets of Northern Ireland. In the end, the young lovers ran away to the Channel Islands and sent everyone a postcard announcing they were married.

At the time, living as a minority Protestant in a Catholic town didn't seem easy. But now I realise just how lucky I was.

Unlike those brought up in Protestant and Catholic enclaves, surrounded only by those of their own religion, and steeped in sectarianism, I learned early on to respect other people's beliefs and cultures, to understand both sides of the argument and tolerate differences.

My segregated school was highly thought of academically, but I am more grateful for my wider education, living among such good friends from both sides in the middle of a divided community.

I saw too many impressionable youths slide into terrorism, often because they knew no better, their values distorted by a sick and twisted society.

When I left Northern Ireland, at 18, to go to university in England, I saw another world. No one cared what religion I was, the tolerance was palpable. Every time I go back now, I realise how much further removed I am from the divisions and hatred I grew up with. I was stunned when I met up with a good friend, a Protestant midwife, a few years ago. Driving through a Catholic area, she chucked rubbish through the window, announcing bitterly: "They can have it, I save my litter for these streets."

It astounded me that an intelligent, well-balanced, normally fairly tolerant person could behave like this. She was under a lot of stress. The Troubles had flared up again, her husband, a policeman, had been injured when his van was blown up and she lived with the pressure that terrorists living in their midst could target him at any time.

It was as if, after being worn down by years of violence and pressure, she succumbed to the deeply-ingrained bigotry instilled in her from childhood.

When I reminded her of what she did recently, she said she couldn't remember, and would never do such a thing. It was as if she had just blanked it out. This may have been a small incident, but it illustrates how people can behave out of character when under such pressure.

The behaviour outside the Holy Cross school is, of course, much, much, worse. Sadly, it is probably too late now to re-educate many of those people so bigoted and disturbed that they will intimidate and terrorise four-year-old infants. But it is not too late to teach the next generation tolerance and understanding.

Schools have a vital role to play. Some integrated colleges have been set up in recent years, although they cater for only three per cent of Northern Ireland's children. But they are a start.

The children of Ulster are its best hope for the future. They deserve to grow up in a climate free from the fear and the prejudice that has scarred the lives of their parents.