Pope Benedict XVI stunned the Roman Catholic church on Monday as he announced his intention to carry out the first papal resignation in almost 600 years, prompting shock from even his closest confidants and acerbic judgment from critics of his eight year-long reign.In an address read out in Latin before a group of cardinals in the Apostolic Palace, the 85-year-old pontiff said he had decided that, due to his “advanced age” and deteriorating strengths, he would be stepping down as head of the Catholic church on 28 February.

“The pope has just broken a taboo by breaking with several centuries of practice,” Cardinal André Vingt-Trois, archbishop of Paris, told journalists, hailing the move as a “liberating act for the future”.

The dramatic move – almost entirely unexpected – paves the way for a successor to be chosen by Easter. Whoever is named the next pope by a conclave next month will inherit a church struggling with many of the same controversies that blighted Benedict’s papacy, from clerical sex abuse to fears over inadequate money laundering controls.

Benedict said he had taken the decision to resign “with full freedom” and great awareness of the “seriousness of this act”. In order to fulfil the role of pope, he said, “both strength of mind and body are necessary, strength which in the last few months has deteriorated in me to the extent that I have had to recognise my incapacity to adequately fulfil the ministry entrusted to me”.

A Vatican spokesman, Federico Lombardi, insisted the pope had “no current illness that would influence his decision”. The Vatican newspaper, L’Osservatore Romano, said he had made up his mind nearly a year ago after trips to Mexico and Cuba in March left him tired. His 89-year-old brother, Georg Ratzinger, told reporters: “Age is weighing on him. My brother would like more rest at this age.”

The German, who in 2005 was the oldest man to be elected pope in almost 300 years, will now become the first pope to resign his position since Gregory XII in 1415 and the first to have done so voluntarily since Celestine V in 1294.

Fears that a papal resignation could cause a schism in the church are generally thought to have deterred previous popes from stepping down, but Lombardi insisted there would be “no risk” of this happening as canon law specifies that a former pope has no right to govern.

Around the world, leaders expressed surprise and sorrow at Benedict’s departure. David Cameron said the outgoing pope had “worked tirelessly to strengthen Britain’s relations with the Holy See”, while Barack Obama said in a statement that he had “appreciated our work together over these last four years”.

The leader of England and Wales’ Roman Catholics was not given warning of the resignation. “Pope Benedict’s announcement today has shocked and surprised everyone,” said the Most Rev Vincent Nichols, archbishop of Westminster.

Nichols, who described the pope’s decision to stand down as one of “great courage and characteristic clarity of mind and action”, said Benedict recognised both the challenges facing the church and the “strength of body and mind” required to deal with them. “I salute his courage and his decision,” he said “I ask people of faith to keep Pope Benedict in their prayers.”

Glowing tributes, however, were not ubiquitous. Victims of the sex and child abuse scandals that erupted under Benedict’s papacy either accused him of being directly complicit in a conspiracy to cover up the thousands of cases that have come to light over the past three years, or of failing to stand up to reactionary elements in the church who were resolved to keep the scandals under wraps.

Norbert Denef, from north Germany, who was abused as a boy by his local priest for six years and was later offered €25,000 (then £17,000) by his diocesan bishop to keep quiet, said: “We won’t miss this pope.”

In and around the Vatican, the view was unsurprisingly more positive.

Luke Doyle, a seminarian from Kansas studying at the American College in Rome, said he was saddened by the news. But, he added: “This decision by the holy father fills me with admiration for him, and a deeper respect.”

Once he stands down, Benedict will be taken to Castel Gandolfo, the papal summer retreat near Rome, and will subsequently live in a cloistered monastery. In his statement he said he wanted to “devotedly serve the holy church of God in the future through a life dedicated to prayer”.

His departure will set in chain the process designed to choose his successor from those candidates who are deemed papabile, or suitable for the papacy. Unlike some previous occasions, there are no obvious frontrunners, but Cardinal Angelo Scola, archbishop of Milan, and Cardinal Marc Ouellet, the Canadian prefect of the Congregation for Bishops, are thought to be among the most plausible candidates.

Benedict will not himself vote in the conclave, in which all cardinals under the age of 80 will take part.

But his conservative theological influence is expected to make itself felt through the decisions of those cardinals – a large number of whom were picked by the outgoing pontiff.