By Robert Pigott
BBC religious affairs correspondent
Pope Benedict's offer has divided the Church of England
About 600 Church of England priests are meeting later to discuss the Pope's offer for them to join their own section of the Roman Catholic Church.
The priests, from Catholic-minded Anglican group Forward in Faith, are unhappy about the way women bishops are being introduced into the CoE.
They will decide how to respond to Pope Benedict's invitation which could allow them to retain some Anglican practices.
Critics say it may harm the CoE's role in uniting Catholics and Protestants.
Clergy on the "high church" wing of Anglicanism, known for their use of more elaborate ritual in services, are alarmed that the Church of England's historic role in uniting Catholic and Protestant in the same Church may now be in jeopardy.
Father Geoffrey Kirk, one of the leaders of Forward in Faith, said: "It will be my intention whatever happens to become a Roman Catholic.
"I am close to retirement, and I may well choose to defer my retirement in order to see that my parish transfers itself to the Roman jurisdiction, as well as myself."
As the dispute in the CoE about women bishops has intensified, many "Anglo-Catholics" have warned they will transfer to the Roman Catholic Church unless they are given guaranteed access to male alternatives.
In the spectacular setting of St James' Roman Catholic Church in London's Spanish Place, Father Christopher Colven celebrates mass.
Only 13 years ago he was an Anglican priest and says he was brought up to see the CoE as part of a wider "universal" Catholic Church.
Serving in a church that had preserved its Catholic traditions for more than five centuries was central to his faith.
But after the CoE ordained woman priests, he felt those traditions had finally been abandoned and says converting to Catholicism was liberating.
"For me there has always been a tremendous sense of relief. Living as an Anglican - honestly trying to live as a Catholic priest within Anglicanism - involved for me all kinds of compromises," he said.
"Becoming a Catholic.. .it's a very freeing experience."
A few miles across London at St Stephen's and All Hallows in Hampstead, mass is celebrated with exactly the same ritual, ceremony and attention to detail.
St Stephen's is Anglican, but although mass here on the Catholic wing of the CoE is virtually identical to that at St James', its priest, Father David Houlding, has a different goal.
He is desperate to preserve the historic character of the CoE inherited from the days of Elizabeth I 500 years ago, as both Catholic and Protestant.
Fr Houlding fears the Pope's invitation could draw away people like him, before a settlement over women bishops is reached and leave behind a more Protestant Church.
He said: "That is my concern of course. I don't want to see that happening. I fear it might. It's not my agenda but it could happen.
"[The Catholic tradition] is important to the identity of the CoE. That's what we are fighting for... we are fighting for the identity of the CoE".
Evangelical Anglicans have also criticised the Vatican's initiative, some even accusing it of capitalising on Anglican disputes to try to poach the Church's clergy.
Others have questioned the way Anglican leaders were informed about it little more than two weeks ago.
Rowan Williams was reportedly only told of the initiative two weeks ago
In Saturday's Times, former Archbishop of Canterbury Lord Carey says he is appalled that his successor Rowan Williams may have had only a fortnight's notice.
"I think, in this day and age, this was inexcusable that Rome decided to do this without consultation," he says.
Stephen Trott, a member of the Catholic Group on the Church of England's ruling body, the Synod, told the BBC the announcement had been mistimed, coming just as negotiations over women bishops reached a critical stage and the Church sensed compromise.
"I think it's come as a surprise and even a shock to those most closely involved in the discussions because these have been proceeding and making progress," he said.
"This announcement seems rather untimely given our discussions."
The Vatican said it was simply responding to approaches by Anglicans in search of a spiritual home.
However, the Roman Catholic Church might not be quite the haven they expect.
CoE clergy would probably lose their houses and church buildings, and it is unlikely many would take their entire congregations with them.
Mr Trott said former Anglicans were likely to be able to use a revised edition of the Anglican prayer book, with services such as Evensong and Matins.
But he said it was doubtful how far they could preserve a genuinely "Anglican identity" in the Catholic Church.
"I think that when people look at the offer, it isn't really very different from what is already available to someone wanting to become a Catholic," he said.
"Already the terms of the offer as published on the Vatican website indicate... that it would really be limited to some parts of the forms of worship that the CoE uses - the Book of Common Prayer - and I don't know whether that would be enough to persuade many people to leave the CoE."
There could be implications for the Roman Catholic Church too.
An influx of highly-educated, relatively conservative priests with a tradition of warm and lively relations with parishioners could create an enclave able to compete powerfully with existing Catholic parishes.
Fr Kirk says married newcomers might also make Catholics question whether their priests need to be celibate.
"Many married clergy coming in from the Anglican Church to the Roman Church with their wives will raise yet again the issue of clerical celibacy in the Roman Church," he said.
Some are wondering whether the arrival of new Catholic-Anglicans could yet turn out to be a Trojan horse, bringing as much change to the Roman Catholic Church in England and Wales, as their departure causes to the CoE.