The Archbishop of Canterbury Rowan Williams and Pope Benedict XVI, respective leaders of the global Anglican Communion and Catholic Church, addressed issues of Christian unity on Friday during a rare joint appearance.

The leaders' meeting comes on the occasion of Benedict's first official state visit to the United Kingdom, which is also the first time a pontiff has travelled to the country in twenty years.

Speaking to an audience of Anglican and Roman Catholic bishops, Williams declared the clergy's "one and indivisible" task as being to "preach the Gospel and shepherd the flock of Christ…[which] includes the responsibility not only to feed but also to protect it from harm."

"Today, this involves a readiness to respond to the various trends in our cultural environment that seek to present Christian faith as both an obstacle to human freedom and a scandal to human intellect," Williams said. "We need to be clear that the Gospel of the new creation in Jesus Christ is the door through which we enter into true liberty and true understanding: we are made free to be human as God intends us to be human; we are given the illumination that helps us see one another and all created things in the light of divine love and intelligence."

Williams added that Christians will be "effective defenders or proclaimers" of the faith when they can "show what a holy life looks like, a life in which the joy of God is transparently present."

"And this means that our ministry together as bishops across the still-surviving boundaries of our confessions is not only a search for how we best act together in the public arena; it is a quest together for holiness and transparency to God, a search for ways in which we may help each other to grow in the life of the Holy Spirit," he said.

Benedict went on to address the topic of Christian unity, which he said is "born of nothing less than our faith in Christ."

"The Church's unity, in a word, can never be other than a unity in the apostolic faith, in the faith entrusted to each new member of the Body of Christ during the rite of Baptism," the pope said. "It is this faith which unites us to the Lord."

Benedict further challenged Anglicans and Catholics in Britain to "rediscover their shared legacy, to strengthen what they have in common, and to continue their efforts to grow in friendship."

The service was held in the midst of some fresh tension between Anglicans and Catholics, which arose at the end of 2009 after Benedict introduced a set of provisions allowing Anglican priests to enter full communion with the Catholic Church – a move that some Anglicans believe is an attempt at "poaching" disaffected clergy who have threatened to leave the Anglican communion over policies related to allowing homosexuals and women to serve in ministry.

Williams, who has been largely unpopular with conservative Anglicans, has defended Benedict's invitation, calling it the fruit of decades of ecumenical dialogue.

Benedict, meanwhile, will conclude his visit to the United Kingdom on Sunday when he will beatify Cardinal John Henry Newman at Crofton Park in Birmingham.