Robyn Hewatt and Andrew Downie were married with all the trappings of a traditional Scottish wedding: Hewatt’s father walked her down the aisle; she had maids of honour and Downie had a best man. A piper played at the door.

But there was no priest, minister or registrar to lead the ceremony. Like thousands of Scots, Hewatt and Downie were legally married by a humanist celebrant. For the first time last year, in what was once a famously religious country, the Humanist Society of Scotland married more people than the Church of Scotland.

Hewatt, 29, a gym instructor, and Downie, 34, a manager with the Screwfix chain, said their wedding on Saturday fitted their identity. “We felt we could make it more personal to us and our story. A humanist ceremony spoke more to us than a more traditional religious type of ceremony,” Downie said.

The catalyst for this dramatic shift came in 2005 when the then registrar general of Scotland changed the law on human rights grounds to allow humanist celebrants to conduct weddings.

Scotland categorises humanist weddings as a non-religious belief ceremony, with the same legal status as church-based and civil marriages. Humanists include atheists and agnostics, and those who say they are spiritual but who dislike organised religion. They embrace same-sex marriage, too, unlike most mainstream churches.

And since 2005 they have mushroomed: in 2017, there were 5,912 humanist weddings with 3,283 conducted by Humanist Society celebrants compared with just 3,166 by the Church of Scotland.

With couples barred from legally marrying with a humanist wedding in England and Wales, some now travel to Scotland to be married, and at least four humanist celebrants from England are hoping for approval to carry out legal marriages in Scotland.

Hewatt and Downie were married by Caroline Lambie, 47, who was brought up in the Scottish Episcopalian church, a branch of Anglicanism, before deciding at an early age she was agnostic. Lambie was herself married at a humanist wedding in 2007.

“Being secular makes sense for most couples I work with,” she said. “These couples say to me that they would feel hypocritical if they did have a church wedding as they have no religious beliefs.”

Prof Callum Brown, a historian at the University of Glasgow and an expert in secularism, believes the country has the highest rate globally of humanist weddings. “Scotland is leading the world in non-religious belief weddings,” Brown said. “I know of no other country where it is anywhere near so high.”

The HSS published new data on Tuesday showing that 59% of Scots now identify as non-religious, with a similar number saying they never attend churches except for someone else’s wedding or a funeral.

The Survation poll for HSS found that 69% of all under-44-year-olds were non-religious, in a country famous as the birthplace of the Protestant theologian John Knox, sectarian rivalries between Protestant Rangers and Catholic Celtic football clubs and staunchly Sabbatarian Presbyterians in the Outer Hebrides. Only among the elderly, those above 65, did a majority believe in a god.

This summer humanist weddings were legally recognised for the first time in Jersey and in Northern Ireland – a place still dominated by religious faith, heaping further pressure on ministers in London to finally authorise humanist weddings in England and Wales.

Humanists UK, the body which covers England and Wales, is planning to take the UK government to court on human rights grounds in an effort to force reform.

Andrew Copson, the chief executive of Humanists UK, said: “The continual failure to recognise humanist marriages in England and Wales not only makes these jurisdictions seem antiquated compared to the rest of the country, but fails to uphold the principle of equality embedded in our human rights settlement.”

Brown said the decline in religious weddings and church attendance generally could be seen across Europe and the industrialised west, especially among whites. It was fuelled first by the advancement of women’s rights in the 1960s, which increased women’s education and economic independence.

More couples chose to cohabit, never marrying or doing so later in life, he said. Progressively fewer people attend church and fewer still have their children baptised. He added Scotland had a long tradition of Sunday opening for shops, something liberalised in England and Wales only relatively recently.

Brown saidthe rate of decline in religious involvement in Scotland had been far faster and more pronounced than in other parts of the UK. It had experienced “a dramatic change from the closed-mind Presbyterianism” which once dominated Scottish life, he said.

Official data from the National Records of Scotland and the Office for National Statistics underline that. In 1961, there were 40,562 weddings in Scotland, with more than half conducted by Church of Scotland ministers. Last year, there were 28,440 weddings overall: more than half of those were civil ceremonies with only 11% by the Church of Scotland.

The Roman Catholic church conducted 1,182 marriages in Scotland last year, compared with nearly 7,000 in 1961 and nearly 2,000 a year a decade ago. In 2016, according to one authoritative survey, only 7.2% of Scots went regularly to church. A large majority of those were over 65.

While marriage rates have fallen too in England and Wales, down by 26% between 2004 and 2015, the Church of England still carried out 43,000 weddings, or 18% of the 244,000 which took place in 2015.

Churches are privately critical of the humanist trend, suggesting it is a pick-and-mix form of consumerism, sometimes using Christian iconography such as crosses even though humanist events are intended to be secular.

Yet Rev Dr George Whyte, the principal clerk at the Church of Scotland, said his church had failed to market its increasingly liberal approach to weddings. The Church of England, by contrast, has a slick and cheery website devoted to selling its religious marriages: yourchurchwedding.org.

Whyte pointed out that couples no longer needed to be members of the church; vows could be personalised and marriages conducted outside the church. There are no longer rules stipulating brides needed to enter first or be given away by their father.

“It’s undoubtedly true that fewer people attend church than 50 years ago,” Brown said. “I suspect the Church of Scotland has been complacent in the sense of presuming that people will always come and ask, rather than us going out and offering, and I think we are waking up to the fact that we need to go out [to sell] rather than stay in.”