Humanist weddings in Scotland are poised to overtake Church of Scotland services, according to the country's biggest humanist organisation.

The Humanist Society Scotland says the decline in religious services and the rise in secular alternatives mean humanist services will soon be the more popular of the two.

The most recent Registrar General's Report, for 2011, shows there is still a considerable gap between Church of Scotland and humanist services but the number of couples choosing the humanist option is rising rapidly. There were 434 in 2006 but the total rose to 2486 in 2011 – a 400% increase over five years. The number of religious services has declined from 16,890 in 2003 to 14,043 in 2011.

Civil marriages remain the most popular – there were 15,092 in 2011.

Steve Chinn, general secretary of the Humanist Society Scotland, said the figures reflected huge changes in society.

"If you look at where those trends are going, on any reasonable basis, at some time in the next couple of years humanist weddings are likely to overtake the Church of Scotland and become number two after registrar weddings," he said.

Mr Chinn said he believed the change was due to a general decline in religious belief but also a feeling couples could design a service just for them if it was humanist rather than religious. "Most people choose humanist because it can be anywhere you like, as long as it's safe and dignified, and secondly because it's really all about celebrating the couple. People want it to really mean something and the humanist wedding is, as we say, all about you."

Mr Chinn said the trend also reflected deeper changes in Scotland. "This change is symptomatic of a good thing, which is that people are becoming less dogmatic and more liberal and more tolerant and open."

Anne Widdop, a humanist celebrant with Fuze Ceremonies, said she believed churches would have to respond to the trend. "I think some already are – the registrars are, and some are offering more in their ceremonies. They need to change."

Ms Widdop believes Scotland has become more secular but that couples want something different from the kind of weddings their parents had.

"The trend in weddings is that they are getting smaller and more intimate," she said. "People want something that is about them and is personal."

She said even some religious people were opting for humanist services. "I've married couples who are church-goers but they wanted a humanist wedding. They said that if they had gone to their minister, they would have had no say in what happens."

The Church of Scotland points out that according to the most recent national census, 65% of Scots identify with the Christian faith and the Church of Scotland has the largest allegiance.

A spokesman said: "Many couples decide to begin their married lives with the blessing of a service in the presence of God. The Church of Scotland extends a warm welcome to couples who on reflection choose a time-honoured service which may have been the choice of their parents and grandparents before them."