Scottish Anglicans are fighting off a split this week as they prepare to be the first British church to legalise gay marriage.

In anticipation of the vote on Thursday in Edinburgh the conservative Anglican grouping GAFCON are expected to announce Rev Canon Andy Lines as a new 'missionary bishop' for Scotland, sources have told Christian Today.

The move will come within hours of the vote, which is expected to pass on Thursday afternoon, and will trigger a rupture with Canon Lines offering alternative leadership for traditionalist parishes in Scotland who oppose gay marriages in church.

The new role will rival existing church structures in the UK with priests having the option to defect and come under the oversight of Lines rather than their official local bishop.

Announcing the move a GAFCON communiqué in May said: 'Faithful Anglicans in Scotland will need appropriate pastoral care.'

The SEC has responded by saying the prospect of a rival bishop is 'regrettable' and breaches the understanding that each Anglican province is autonomous.

Most Rev David Chillingworth, primus of the SEC, said: 'The outcome of the synodical process which will take place in June is not a foregone conclusion. The voices of clergy and lay people from across Scotland will be heard both in debate and in the voting process.

'The Scottish Episcopal Church is working closely with those who find this proposal difficult to accept. Whatever the outcome may be, it is our intention to be and to remain a church which honours diversity.'

Canon Lines is currently chair the fringe church network Anglican Mission in England and part of GAFCON UK's taskforce. He is also director of the missionary society Crosslinks.

The announcement of a rival 'missionary bishop' comes as SEC leaders prepare recommend that priests be allowed to preside over same-sex marriages.

The major chance in church teaching is thought to pass with the required two-thirds majority in all three of the general synod's 'houses' – the laity, the clergy and the bishops.

Synod members are expected to pass that motion that removes the understanding of marriage as 'a physical, spiritual and mystical union of one man and one woman'.

The teaching will read: 'In the light of the fact that there are differing understandings of the nature of marriage in this Church, no cleric of this Church shall be obliged to conduct any marriage against their conscience.'

Rev David McArthy, a traditionalist priest in the SEC and part of the conservative Scottish Anglican Network, told Christian Today there was an 'immense sadness from many people in Scotland' about the upcoming decision.

'It is not simply a group of evangelical churches who have concerns about this but a fairly wide group,' he said.

'I pray that the leadership realise what they are about to do will have serious consequences for the church.'