A detailed analysis of population trends, disclosed for the first time by the Independent on Sunday, shows that the degree of physical separation between Protestants and Catholics is increasing year by year, with the number of segregated areas more than doubling in the last two decades.
Increasingly, large sections of the population are literally strangers to one another, a fact with ominous implications for the Government's hopes of finding political accommodation.
The analysis of Northern Ireland's 566 district council wards, drawn from unpublished data in the 1991 census, shows that:
About half of the province's 1.5 million population live in areas more than 90 per cent Protestant or more than 90 per cent Catholic
Fewer than 110,000 people live in areas with roughly equal numbers of Catholics and Protestants. Analysis of the data often reveals that an apparently mixed ward contains two separate communities, sometimes physically parted by 20ft-high reinforced walls known as 'peace lines'
In the past two decades, the number of predominantly Catholic wards increased from 43 to 120. Areas almost exclusively Protestant rose from 56 to 115
Of Belfast's 51 wards, 35 are at least 90 per cent of one religion or the other.
News of the survey startled political leaders. John Alderdice, leader of the non-sectarian Alliance Party, said: 'It's polarisation, and most worrying. It's almost creating an apartheid situation.'
Chris McGimpsey, a senior figure in the Ulster Unionist Party, said: 'We're effectively splitting into two separate and distinct communities here. I see apartheid in Belfast. When a community turns in on itself, meeting less and less of the other community, they have less knowledge of them as human beings. That that certainly increases the potential for sectarian violence.'
The new data shows that segregation is widespread across both urban and rural areas, but that it is at its worst in the two main cities, Londonderry and Belfast. In the first, a once substantial Protestant presence has virtually disappeared from the west bank. In Belfast, substantial religious integration exists in only two middle-class pockets in the north and south. Even here, however, the mixing may be only temporary in that these were once Protestant but are now becoming more Catholic.
While divisions are most conspicuous in working-class parts of north and west Belfast, where the 'peace lines' carve through streets, the east of the city is less obviously but just as effectively segregated, as it fills up with Protestant middle-class families.
Thus wards in the plush areas around Stormont Castle, the seat of government, and the nearby police headquarters, are up to 98 per cent Protestant. This has important implications for the administration, as many senior civil servants live in these areas.
A Catholic senior civil servant, asked whether his Protestant colleagues lacked insight into life in the segregated areas, replied: 'With some, their ignorance is total. You have people determining housing policy who have never been on the Shankill Road or the Falls Road.'
On a human level, the geographical divisions mean that people can, in a fashion that seems natural to them, lead lives of near-apartheid. One Catholic woman who recently married an east Belfast Protestant says she realised, after an evening with his neighbours, that she was the first Catholic that most of them had ever met socially.
She commented: 'They treat me so carefully, so cautiously, skirting round anything to do with the troubles. Several times I've been asked, 'When did you come up here?'. They assumed I was from the Republic - they just couldn't conceive I'd been born and brought up in Belfast.'
A middle-class Protestant recalled playing with Catholic children when he was a boy: 'We knew what religion we were all right, but we played anyway. Now my kids don't really meet Catholics at all.'
While there are various social, sporting, cultural and other contacts across the divide, 24 years of violence have served to deepen existing divisions. Most Protestant children continue to be educated in state schools while most Catholics go to schools run by the Catholic church. Fewer than 1 per cent of children attend integrated schools.
In employment, some progress has been made towards equal opportunity. But more than 250 sizeable firms still have workforces which are virtually or completely segregated.
In mixed workplaces, people of different religions tend to observe the unwritten but widespread rule that religion and politics are simply too sensitive to be discussed in mixed company. One well-known catchphrase is: 'Whatever you say, say nothing.'
Although segregation is recognised as a deeply unhealthy state of affairs, the Government, housing authorities and security forces have been unable to reverse the trend towards greater and greater separation.
One official said: 'People do this for security. It's generally fear. And you can't insist to somebody that they live somewhere that's mixed, especially when they fear for their lives.'
A government source commented privately that there were two policy approaches which were in fact at variance. He said: 'On the one hand general government social policy would theoretically favour a mix. But then security policy would probably favour a separation because it keeps things distinct and easier to control.'