The move comes weeks before the "global south" conservative Anglican leaders meet in Alexandria, Egypt, to discuss their continuing programme of opposition to gay rights. Some sources say that this meeting could mark the start of the formal process of schism, with a new Anglican communion being founded to represent orthodox Anglicans.

Communion with Canterbury is regarded as one of the defining characteristics of Anglicanism. The Nigerian Primate, Dr Peter Akinola, has previously said that it is not necessary to go through Canterbury to get to Christ. According to a statement posted on the Anglican Church of Nigeria website, it has now decided to make this official and has "redefined" its relationship with all other Anglican Churches.

Any references to "communion with the See of Canterbury" have been deleted from the constitution. Instead, the Nigerian Church is defining itself as in communion with Churches, dioceses and provinces that uphold the "historic faith, doctrine, sacrament and discipline of the one Holy, Catholic and Apostolic Church". This will certainly rule out the pro-gay Churches of the US and Canada. It will probably also exclude the Church of England.

The Nigerian Church is one of the biggest and is the fastest growing in the communion. It is strictly evangelical and does not ordain women. Dr Akinola recently started a missionary campaign to double the 17.5 million members by 2007 with the aim of making Anglican Christianity the country's leading religion within a few years.

But his ambitions extend beyond the borders of Africa. Further changes in the constitution allow Nigerian missionaries for the first time to create Anglican "chaplaincies" outside Nigeria.

The newly formed Convocation of Anglican Nigerians in Americas will now work on setting up a network of Anglican chaplaincies across the US to give "refuge" to conservative evangelicals unhappy with the consecration of Gene Robinson, who is gay, as Bishop of New Hampshire, and other liberal developments.

Dr Williams's office was not available for comment last night.

One US insider said that the response was not one of despair but of relief. He said: "This is the most serious development so far, but the reaction here is straightforward. It is one of relief. The one thing that defines us is being in communion with the See of Canterbury. There is nothing else.

"We are not a confessional church. We are relieved because we cannot have the threat of a breach being held over us forever. It is as if the divorce has come through."

Canon John Rees, a leading canon lawyer and provincial registrar for the Canterbury Province, played down the significance. Although Nigeria is the first to delete deliberately the mother church, Canon Rees said several other of the 38 provinces already made no direct reference to Canterbury in their constitutions.

He said: "I do not see a difficulty. It does not seem to me to change the legal position at all. There is nothing in what they have done that suggests to me that a clergyman from Nigeria would no longer be able to come and function in the Church of England in the same way that they might have done the day before yesterday. And this is an example of what communion means."

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