History will be made today when the Church of England's General Synod is addressed by the Presbyterian Church of Scotland's General Moderator.
It is believed to be the first time a serving moderator has been invited to speak to the Church of England's governing body. Synod will be asked to accept a new agreement between the Church of England and the Presbyterian Church of Scotland.
The Columba Declaration commits the two national churches to "grow together in communion and to strengthen our partnership in mission" and will be debated in Synod following the presentation from Church of Scotland General Moderator, Rev Dr Angus Morrison.
The proposed agreement foresees "fuller unity" as ministers will be invited to "exercise ministry in the other Church, in accordance with the discipline of each Church".
However Morrison's address at Synod today will not be entirely welcomed, particularly by the Scottish Episcopal Church (SEC) who are "deeply hurt" by the new agreement.
The SEC's Primus, the Most Rev David Chillingworth, said the agreement would cause "real difficulty" between his Church and the CofE. He also questioned whether it was "proper" for CofE to enter an agreement about "ministry and ecclesiastical order" in a part of the UK where it had no official jurisdiction.
Members of Synod are also said to be unconvinced about the necessity of the agreement to be debated on Tuesday morning. They will be asked to welcome the Columba Declaration and a co-authored report by the two churches as "a significant development in the relationship between the two churches".
The Church of Scotland will debate the proposals at their gathering in May.
Speaking ahead of his Synod address, Morrison said: "I feel it a real honour to be invited as moderator to address the General Synod.
"Through the historic Columba Declaration we are proposing to commit ourselves to growing further in communion and to strengthening our partnership in mission.
"By formally recognising the long ecumenical partnership between our churches, I believe we will advance our shared mission of spreading the Christian message of the Gospels."
During his time in London, Morrison will stay with his wife at Lambeth Palace. Morrison said it "will be a great pleasure to stay at Lambeth Palace" and added they were "looking forward to renewing our relationship with Archbishop Justin and Mrs Welby".