In a 20-minute meeting on Saturday Dr Williams complained to the Pope about the lack of consultation which had left him in an "awkward position".

A day before their meeting Archbishop Vincent Nichols of Westminster told a press conference in London that the bishops had agreed at their November meeting in Leeds to appoint a commission to try to iron out obstacles to the group reception of Anglicans.

It will include Auxiliary Bishop Alan Hopes of Westminster, the most senior Anglican clergyman convert in the Catholic Church in England and Wales, as well as Archbishop-elect Bernard Longley of Birmingham and Bishop Malcolm McMahon of Nottingham, all of whom are highly experienced in ecumenical dialogue.

Archbishop Nichols said: "The Apostolic Constitution gives us the end game but not the process. It is up to us, working with the Church of England, to look at the process."

He added that Dr Williams had already ruled out the purchase of Church of England buildings as "impossible".

The defection of large numbers of Anglo-Catholics grew increasingly likely after traditionalists failed to secure concessions over women bishops to help them to stay in the Church of England. The General Synod's revision committee rejected proposals for a structure that would allow them to be served by "flying bishops" in preference for a "code of practice".

Forward in Faith, the largest Anglo-Catholic group, has estimated that 450 parishes are considering the Pope's offer and as many as 200 of them might accept it.

Anglican Bishop John Broadhurst of Fulham, chairman of Forward in Faith, said: "We have 1,000 priest members in my organisation and there are many others who agree with us. The main issue for many Anglican priests is now the ownership of parish churches."

Understanding the attachment of Anglo-Catholics to their church buildings, many of which are listed or historic, the Catholic commission is expected to look at the possibility of church-sharing and also the chances of taking out 100-year leases of some Anglican parishes, including a commitment to maintain and repair them.

Fr Anthony Symondson, a former Anglo-Catholic vicar who became a Jesuit priest, doubted however whether mass conversion was inevitable. He predicted that if an English Ordinariate relies on "shared churches and temporary buildings" he felt it would "represent a very small number of people with a very limited future".

"None of us really know how the Church of England is going to respond to it and how the Church Commissioners are going to respond to it in terms of letting property go," he said. Congregations are likely to be split by the decision and may be tempted to experiment with parish-sharing, he said, but he explained that when this was tried at a church in west London in the 1990s it was soon halted by Cardinal Basil Hume because of divisions between Catholic converts and the resident Anglican congregation.

Fr Symondson added: "A lot of divorced and remarried Catholics go to these churches because they are effectively excommunicated from the Catholic Church and the last thing they want is to be under the jurisdiction of Rome again because it will put them back in the situation that they have tried to escape."

Last weekend the vicar of an Anglo-Catholic church received a threatening phone call warning him of violence if his parish converted. His noticeboard had the words "C of E No Pope" daubed across it in white paint. Fr David Waller of St Saviour's, Walthamstow, east London, discovered the vandalism on Sunday morning.

In spite of tensions, both the Pope and Dr Williams publicly reaffirmed their commitment to "consolidate the ecumenical relationship". The pair also discussed the third round of study by the Anglican-Roman Catholic International Commission (ARCIC), the body for theological dialogue.

Dr Williams told Vatican Radio that media presentations of the Constitution as a "dawn raid on the Anglican Communion" were simply wrong. "People become Roman Catholics because they want to become Roman Catholics, because their consciences are formed in a certain way and they believe this is the will of God for them. And I wish them every blessing in that," Dr Williams said.

"But I don't think it's a question of the Roman Catholic Church, as it were, trying to attract by advertising or by special offers."

END