The Archbishop of St Andrews and Edinburgh says the introduction of equal marriage in Scotland may mean Catholics will have to exchange their vows twice.

Archbishop Leo Cushley believes the reform could mean the Roman Catholic Church shifting to joint vows in churches and also at registry offices in Scotland.

He says the changes would be to avoid legal challenges over the Church’s opposition to same-sex weddings – but the comments have been branded as scaremongering by LGBT campaigners.

“You are rolling two things together in one ceremony, the blessing of a union and then the state’s recognition of that union,” Archbishop Cushley added: “There are Catholic countries, like France, where they are two separate things and have been since the French Revolution and the separation of church and state. It’s not impossible to imagine such a thing here in the future … It is, at least, an option that may have to be contemplated.”

In response, David Allison, a spokesman for gay rights group Outrage!, said: “The Catholic Church is thrusting up red herrings about the gay marriage bill because it has been made quite clear that they wouldn’t face legal action from couples.”

A spokesperson for the Scottish Government added: “The Marriage and Civil Partnership Bill contains protections for religious bodies and celebrants. Religious bodies will have to opt in if they wish to carry out same-sex marriage. We have agreed with the UK Government that the Equality Act will be amended to provide further protection for celebrants.”

Currently, the Catholic Church in Scotland performs weddings on behalf of the state, with priests acting as an “authorised person” to marry couples in place of a registrar – and certifying the marriage on an official document.

Over the weekend, Labour MSP Elaine Smith was criticised for mentioning polygamy in the debate for equal marriage in Scotland.

The MSP for Coatbridge and Chryston said there was “no logic” for discriminating against more than two people getting married.

The Marriage and Civil Partnership (Scotland) Bill was introduced in the Scottish Parliament in June, and the first major vote is likely to take place in November, following initial scrutiny by the Scottish Parliament’s Equal Opportunities Committee.

Earlier this month, Archbishop Cushley said he did not believe his disgraced predecessor should return to Scotland.

Cardinal O’Brien stood down as Archbishop of St Andrews and Edinburgh in late February following allegations by three priests and a former priest of improper sexual contact in the 1980s.