Almost 6,000 couples have married in the Dublin registry office to date this year, four times more than in 2000.

The growth in the number of people turning away from church weddings is highlighted in a behind-the-scenes documentary about the registry office, due to air tonight.

Registrars Julie Morgan and Anne Bradley also hit out at the increase in the number of sham marriages occurring in Ireland, and claim couples who can't speak the same language and don't know each other's names are looking to be married.

"We'd have a number of couples coming for a marriage of convenience," Bradley says. "It would be a non-European wanting to marry a European; they feel it would help them remain in Ireland longer than normal. A lot of couples wouldn't have a common language, wouldn't know each other's names or be able to even write each other's names."

Bradley acknowledged that "there isn't a lot" that can be done about the issue.

"When we see people without a common language it raises the question as to why they are coming in here. We do a lot for the couples who come to us and make sure we care for them – every couple is special to us – but for those people who are using marriage as a convenience, it is just hugely disheartening for us. There doesn't seem to be a lot that we can do."

An average of 40 marriages a week now take place in the office, which is attempting to cope with backlogs due to the increase in demand. Meanwhile, Westlife, Boyzone and Shania Twain are the top three wedding-song artists, with Twain's From This Moment the most-used CD.

Bradley and Morgan say the only strict guideline in the office is the use of religious references in vows.

"We encourage people to do their own private vows to make it special for them. However, we will not allow religious content. Most couples are getting married here because they don't want a religious ceremony so we are fairly strict on that side of things, but with everything else we are fairly relaxed."

'In and Out in a Half an Hour airs tonight at 9.30pm on RTÉ One