The Archbishop of Canterbury, Dr Rowan Williams, will be among the guests from the UK's Christian communities at the inaugural Mass for Pope Benedict XVI at St Peter's in Rome on Sunday.

Dr Williams will be only the second serving Archbishop of Canterbury since the Reformation to attend the inauguration of a new Pope. He was the first to attend a Pope's funeral.

Dr Williams will be accompanied by his wife Jane and staff members the Rev Andrew Norman and the Rev Jonathan Jennings. Dr Williams will again wear a ring and a pectoral cross presented to Ramsey by Pope Paul VI.

Anglican officials, heartened by the new Pope's references to ecumenism in his first homily, are expected to use the visit to explore the possibility of a formal meeting between the two, probably within the next two years.

This week Dr Williams offered his best wishes and prayers for Cardinal Joseph Ratzinger on his election as successor to Pope John Paul II. He said: "We wish Pope Benedict XVI every blessing in the immense responsibilities he is about to assume on behalf of Roman Catholics round the world.

"His election is also of great significance to Christians everywhere. I look forward to meeting him and working together to build on the legacy of his predecessor, as we seek to promote shared understanding between our churches in the service of the Gospel and the goal of Christian unity."

Dr Williams accepted the invitation as the Vatican disclosed that Pope Benedict XVI has chosen Cardinal Angelo Sodano as his Secretary of State in his first appointment since becoming pontiff.

Cardinal Sodano served in this key role under the last Pope. Although it was unlikely that a new Pope would have removed him from office, the speed and nature of this announcement, which also confirmed other top officials in their existing jobs, indicates that Cardinal Ratzinger's election was one intended to symbolise continuity with the reign of his predecessor.

Cardinal Sodano's job makes him second in the hierarchy only after the Pope. Congregation prefects will all complete their five-year terms, meaning that any changes under this Papacy will be gradual. At 77, Cardinal Sodano is already two years past normal retirement age for the Vatican's top officials.

Other delegates to Sunday's Mass will include the Archbishop of Westminster, Cardinal Cormac Murphy-O'Connor, who will return to Rome on Saturday after celebrating a special Mass of thanksgiving tonight at Westminster Cathedral.

Neither Tony Blair nor Cherie Blair will be attending. Downing Street will confirm later today who will represent the British Government. The Duke of Edinburgh will represent the Queen.

In total, about 500,000 people along with state leaders and royalty are expected in Rome on Sunday. Guests include Chancellor Gerhard Schröder of Germany and his wife along with the country’s President, Horst Koehler and his spouse, honouring their former Archbishop of Munich.

Jean-Pierre Raffarin, the French Prime Minister, will be accompanied by his Foreign Minister, Michel Barnier. Other European leaders will include the Portuguese Prime Minister, Jose Socrates.

From Latin America, President Alvaro Uribe of Colombia plans to attend the inauguration. The Mass will take place on Sunday at 10am (9am UK time).

The Church of Scotland's Dr Ian Torrance, now president of the Presbyterian Church's largest theological seminary in the US, will be one of two delegates representing the world's 75 million Reformed Christians at the installation.

He accepted his invitation with a welcome to the new Pope, and used the opportunity to plead with him to end his ban on condom use in helping to combat Aids.

Dr Torrance, Moderator of the Kirk from May 2003 to May 2004, said: "For all of the drama and achievement of the late Pope, he tended to polarise church and culture rather than seek common goals. The new Pope may wish to devise constructive ways to welcome the ministry of women, granting it dignity and institutional status.

"It is no longer sustainable to prohibit the use of condoms in countries where HIV and Aids threaten such devastation. How may he honor the vocations and gifts of priests who marry? And then there is a matter of style. Though ascetic and personally humble, it is undeniable that the late Pope projected an imperial image. I hope that style is now a thing of the past."

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