Anglican and Catholic theologians meeting in Rome this week will be examining a new path to possible unity.

After Anglican provinces worldwide began ordaining women priests and bishops, relations between the Roman Catholic Church and the Anglican Communion hit their lowest point in modern times. 

Commentators described it as an "ecumenical winter".

But now, even Anglican women bishops sit around the table with Catholic bishops at high-level talks between the churches. 

And in papers being studied in Rome this week, the word "subsidiarity" is the key to finding a possible way forward.

The climate is now being described as an "ecumenical spring" with even signs of summer in the air.

Archbishop David Moxon, director of the Anglican Centre in Rome, which is celebrating its 50th anniversary this week, told Christian Today that Catholics and Anglicans are "85 per cent" in agreement.

He quoted John 17, when Jesus prays for the disciples: "I ask not only on behalf of these, but also on behalf of those who will believe in me through their word, that they may all be one." 

Seeking to be united as one church is "part of our DNA", he added. The two bodies hold different views on women's ordination. But in talking about "subsidiarity", the theologians and bishops are trying to discern what is essential, core doctrine and what could be said to fall within "reasonable diversity". 

The problem now for those who want unity is discover whether women's ordination could be agreed by both Catholics and Anglicans to be part of a reasonable diversity. "How do we discern what is essential and what is non-essential," said Moxon. 

Already, the churches share a common baptism. "What unites us is greater than what divides us," said Moxon. 

He was speaking on the eve of the third formal meeting between the Archbishop of Canterbury and the Pope  in Rome this week. 

Moxon was present at their first meeting, three years ago and also when they were together in Assisi a few weeks ago. There was an "instant spark" between the two, he said, and soon they were laughing together. "They clearly saw themselves as brothers. They enjoyed each other's company."

And this friendship has continued to grow since that day.

He said he sees the ministry of Pope Francis as prophetic and apostolic. "This Archbishop of Canterbury is in my view the perfect partner for that kind of mission. They are on the same page of the same song sheet."