A prominent conservative Anglican group has issued an unprecedented call for the Church of England to split over the issue of gay marriage.

The chairman of Gafcon, a body of conservative evangelical Anglican leaders and churches, has written a "pastoral letter" encouraging a schism to halt the "contagious" spread of churches welcoming gay marriage.

The influential Nigerian primate, Archbishop Nicholas Okoh, has previously called for the "reform and renewal" of the global Anglican Communion but his most recent letter issued on Tuesday admitted "schisms happen" and appeared to call for a divide over the issue.

He said "bold action" was needed from conservative Anglicans and said that in the desire maintain unity doctrine "respectability has been given to a false gospel".

He wrote: "The English House of Bishops has failed so far to demonstrate that it has the will to resist compromise and I therefore call on Gafcon in the UK and the Anglican Mission in England to demonstrate that they have the necessary courage and faith in a context which to a large extent they alone can grapple with."

Gafcon, or the Global Anglican Future Conference, was formed in 2008 when conservative primates, archbishops and bishops formed a rival meeting to a gathering of Anglican leaders in Lambeth over the issue of gay marriage. Now a prominent force in the worldwide Communion, Gafcon has offered "alternative oversight" to Anglican clergy and congregations in areas where bishops support same-sex marriage.

The call comes after 12 parishes in the south of England announced they would consider whether to sign Gafcon's statement of faith issued after their first conference in 2008.

The meeting, led by Rev Dr Peter Sanlon from St Mark's, Tunbridge Wells, will discuss whether a new Anglican synod should be set up, if Church of England bishops move towards blessing same-sex unions.

Dr Sanlon told the Telegraph: "If senior leaders of the Church of England water down the teaching of the Church of England on key issues like homosexuality, then this synod could easily evolve in to a new Anglican jurisdiction in England. The Archbishop of Canterbury has signalled that he is aware of the possibility that a significant proportion of the church will not accept a change in the church's teaching. This could be the beginning of that playing out.

"I am not leaving the Church of England - but in order to stay, I need new partnerships and structures to discharge the mission of the Church of England, which is to bring the message of Christ to every postcode in England."

The bishops will meet later this year to discuss the next steps after a two year process of "shared conversations" to discuss the issue.

Okoh said the talks have "made matters worse", but the Archbishop of Canterbury has repeatedly spoken of the importance of dialogue and last week said he was "constantly consumed with horror" at how the church treats gay people.