Anglo-Catholic opponents of female priests within the Church of England now estimate the number of clergy who will leave over the matter to be about 250. They hope for concessions to make the transition as painless as possible.
However, Roman Catholic sources say that few concessions will be on offer. The main point at issue is the validity of Anglican priesthood, even for men.
According to the Vatican, there are no priests in the Church of England. All Anglican priestly orders are 'utterly null and void' according to a declaration of 1896. In practice, this anathema is largely ignored.
Anglican priests who convert to Rome must be reconfirmed and then 'conditionally' re-ordained. There are at the moment eight married Roman Catholic priests in this country who started off as Anglicans. None, however, has a parish.
Five Anglo-Catholic priests have written to the bishops setting out some of the difficulties they see in the way of conversion. For a start, they do not like the word 'conversion'.
'Convert' and 'dissident' also cause some offence, they say, 'focusing attitudes of suspicion, resentment and hostility.
'Our people would see a significant difference between becoming a Roman Catholic and entering into full communion with the Holy See.'
It is precisely this difference that Roman Catholics cannot see, and which is one of the major difficulties to be overcome.
The problem for the Roman Catholic side is the suspicion that the Anglicans involved still do not want to become Roman Catholics. They just want to go on being Anglicans without female priests. 'The crucial issue here is not one of doctrine, but of a way of life,' Fr John O'Shea, a parish priest who has been involved in receiving converts into the Roman Catholic diocese of Portsmouth, said.
Many Anglo-Catholics are ready to agree with almost every Roman doctrinal position: they accept the doctrines of the assumption of the Blessed Virgin Mary, the infallibility of the Pope, and transubstantiation.
Their real objection to the Roman Catholic Church is that it is not the thing for them. In the old snobbish joke, it is 'the Italian mission to the Irish', not something for the English middle classes at all.
But the process by which adult converts are now received into the Roman Catholic Church stresses belonging at least as much as believing.
Under the new arrangements, known as the Rite for Christian Initiation of Adults, or RCIA, each convert is given a 'sponsor' - a practising Catholic to act as a guide.
After as many as six months of weekly meetings, the candidates are accepted at a service at the start of Lent, and then confirmed and receive their first communion at the Easter vigil mass on Holy Saturday night.
This year, 2,000 converts were received into the Roman Catholic Church through these rites.
'I would strongly believe that the Anglicans who want to come over should go through it,' Fr O'Shea said. 'They need ample time and preparation. It's not just a quick switch.'
Those of the Anglo-Catholic clergy who have decided to go to Rome are well aware of this. One man - who asked not to be named because he has not yet told his congregation - said he does not believe that his congregation would follow. Although he hopes to become a Roman Catholic priest, he knows there are no guarantees, he said.