It also set out principles concerning lay people entering partnerships, and recommended that they should not be asked about their relationships before being admitted to baptism, confirmation, or communion.

The Act will grant legal recognition to same-sex couples for the first time, giving them legal rights similar to those of married couples. These include rights to property and pensions, and access to a partner's hospital records.

Anglican Mainstream's letter states that the partnerships "are bound to be seen as a form of gay 'marriage'", and that it is "naïve" of bishops to think that those in the Church embarking on a partnership "will eschew sexual intimacy". It says that it will encourage clergy and lay leaders "to place the demands of the gospel before people living in active same-sex relationships by calling for repentance and commitment to live a new life".

The Sheffield branch of the conservative Evangelical network Reform issued its own statement on Friday, calling on "all authentic Bible-believing Anglicans in the diocese not to take Holy Communion with or from clergy who register under the Civil Partnership Act".

Fulcrum, a group set up "to give a voice to those who identify with Evangelicalism's centre ground", also issued a statement last week criticising the Bishops' response to the Act. It says: "It fails to offer a stronger prophetic critique of the Government's clearly stated intention to construct civil partnerships so that they are quasi-marriages.

"This intention and the popular perception of civil partnerships as 'gay marriage' clearly threatens to undermine the status of marriage in British society." Fulcrum is also concerned about the Bishops' view that lay people seeking baptism, communion or confirmation should not be questioned about their relationship.

The provisions of the Civil Partnership Act 2004 come into force on 5 December, which would allow the first partnerships to be registered on 21 December.

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