The British ambassador to the Vatican warned that Pope Benedict XVI's invitation to Anglican opponents of female priests to convert en masse to Catholicism was so inflammatory that it might lead to discrimination and even violence against Catholics in Britain, according to a secret US diplomatic cable.

Talking to an American diplomat after the archbishop of Canterbury, Rowan Williams, met the pope in November 2009, Francis Campbell said the surprise Vatican move had placed Williams "in an impossible situation" and "Anglican-Vatican relations were facing their worst crisis in 150 years as a result of the pope's decision".

Campbell's strikingly candid comments are documented in one of a series of confidential dispatches from Washington's Vatican embassy released by WikiLeaks. Others reveal that:

• US diplomats believed the pope was instrumental in securing the release of 15 British sailors captured and held by Iran in 2007.

• The Vatican refused to allow its officials to testify before an Irish commission investigating abuse of children by priests and was angered when they were summoned from Rome.

• The pope was responsible for the Vatican's resistance to Turkey joining the EU and wanted a reference to Europe's "Christian roots" included in the EU constitution.

The revelations come after 12 days of cable releases by WikiLeaks that have dominated headlines around the world and seen the whistleblowers' website and its founder, Julian Assange, vilified by some US politicians and extolled by others – including free speech advocates and the Kremlin. The Guardian is one of five international news organisations which had exclusive access to the cables.

Campbell, himself a Catholic, made his remarks in a conversation with the American deputy chief of mission to the Holy See, Julieta Valls Noyes, after the pope decided to announce a special dispensation allowing disaffected Anglicans to convert in groups while retaining their own leadership and some of their rites, in a body called an Ordinariate.

This had been arranged in Rome behind the backs of the English Catholic bishops, and Williams was given little warning. An official Vatican statement described the November 2009 meeting between Williams and the pontiff as cordial, but Campbell told the US ambassador, theology professor Miguel Diaz, that it was "at times awkward".

At a subsequent dinner held in Williams's honour and attended by senior Vatican officials, Campbell told Noyes "Anglican-Vatican relations were facing their worst crisis in 150 years as a result of the pope's decision", a cable sent to Washington shortly afterwards revealed.

Campbell said: "The crisis is worrisome for England's small, mostly Irish-origin, Catholic minority. There is still latent anti-Catholicism in some parts of England and it may not take much to set it off." He warned: "The outcome could be discrimination or in isolated cases, even violence, against this minority."

The ambassador told Noyes the decision had shifted the goal of the Catholic-Anglican ecumenical dialogue "from true unity to mere co-operation" and claimed that some Vatican officials believed the pope had been wrong not to consult the archbishop before making the announcement.

The cable continued: "The Vatican decision seems to have been aimed primarily at Anglicans in the US and Australia, with little thought given to how it would affect the centre of Anglicanism, England, or the archbishop of Canterbury. Benedict XVI, Campbell said, had put Williams in an impossible situation. If Williams reacted more forcefully, he would destroy decades of work on ecumenical dialogue; by not reacting more harshly, he has lost support among angry Anglicans."

Reporting back to Washington, the US diplomats wonder "whether the damage to inter-Christian relations was worth it – especially since the number of disaffected Anglicans that will convert is likely to be a trickle rather than a wave".

Out of the Church of England's 114 bishops, three have since announced that they will be joining the new Ordinariate, joined by two retired ones. All of them are long-standing opponents of female priests. It is expected that they will be joined by 50 of the church's 10,000 priests with elements of their congregations.

In a separate conversation, Campbell warned Diaz that if many Anglicans decided to convert, the Catholic church in Britain could find itself financially stretched. "Campbell cited the difference between the Anglican stipend and Catholic allowance as chief among them," according to another cable to Washington. "Because of the need to provide for families, Anglican priests are paid far more than their Catholic counterparts. With many parishes already financially stretched, a large transition of Anglican converts could overwhelm the financial resources of many dioceses."

The Catholic church is to set up a fund to finance the Ordinariate in its early days.