Today's tough economic reality has prompted urgent action from the Church of Scotland to make its pensions scheme sustainable.

Pensions trustees explained to the Kirk's General Assembly today that volatile financial markets and longer life expectancy mean the current system is no longer viable.

Commissioners heard that the Kirk is sitting on a pensions deficit of £29.1m that needs to be paid for.

Pensions trustees have been working with the Church of Scotland's four employing agencies to ensure that the deficit repayments are manageable.

The Church is now in the process of consulting some 3,500 ministers and employees on proposals to change from a salary based pension scheme to a defined contribution scheme.

"We will take full account of what staff say," said Pauline Weibye, Secretary to the Council of Assembly.

Addressing the Church of Scotland General Assembly, Convener of the Council of Assembly the Reverend Grant Barclay warned that the work of the Church would be "adversely affected" if the pensions scheme was not changed.

"The Council of Assembly together with the employing agencies has taken seriously the warnings about future pensions funding highlighted by the pensions trustees at last year's Assembly … Current arrangements are unaffordable," he said.

In comments after the Assembly session, Mr Barclay added that any proposed changes to the schemes would not affect benefits already accrued by active members of the scheme or the pensions of those who have already retired.

The changes are due to come into effect by no later than 1 January 2014.

Mr Barclay added: "The Church remains committed to providing a secure pension structure for the future and to consult with staff on the proposals."