The Archbishop of Canterbury will be the first head of the Church of England to join a debate at the Church of Scotland's General Assembly on Wednesday.

Archbishop Justin Welby will address the Church's ruling body on a key report that proposes formal links between the two Churches.

The agreement, known as the Columba Declaration, was passed at the Church of England's synod in February but is yet to be ratified north of the border. If passed, the Columba Declaration would allow clergy to minister in the other's churches, and would formalise an agreement to move "towards fuller communion".

The former moderator of the Church of Scotland, Angus Morrison, said he was "confident" the Assembly would pass the Declaration.

"In itself the Declaration is largely of a symbolic nature but it does pave the way for our further growth in fellowship and for extending partnership in mission as sister and national churches who share many common roots, challenges and opportunities," he said.

"We wish this to happen in the closest possible fellowship with other sister churches in the United Kingdom as we seek together to address the challenges of mission in our country today."

However the move is not without controversy. Although the Church of Scotland is the national Church of Scotland, as the CofE is in England, the CofE has existing links with another Scottish Church, the Scottish Episcopal Church (SEC).

The SEC is already linked to the CofE in the Anglican Communion and is unhappy with the new agreement. A rift emerged after the SEC withdrew from discussions between the three Churches over the Declaration.